Roem, 33, has focused mostly on local issues in her quest to unseat incumbent Del. Robert G. Marshall, a Republican who has represented Prince William County for more than two decades.
The fact that Marshall is an outspoken conservative, who has proposed regulating transgender bathroom use and refuses to use female pronouns in reference to Roem, has only stoked interest from advocacy groups.
Roem, a former newspaper reporter, has played the celebrity to her advantage, drawing donations and headlines from across the country while outraising Marshall by a margin of more than 3 to 1.
While her appeals to voters are heavy on proposals to reduce traffic, create jobs and update infrastructure, Roem also talks passionately about the possibility of making history:
"It is long past the time for [Marshall] to be defeated by someone who will champion inclusion in Virginia," Roem said.
"And I'll do it."
'I don't know if he'd be proud'
The Democrat's journey has been long but mostly local.
Roem was 3 years old when her father, John Paul Roem, took his own life two days after Christmas. Her maternal grandfather, Anthony P. Oliveto, became a father figure. Oliveto was a gruff Italian American World War II veteran who loved baseball. And so young Roem also took up the sport, playing second base for Little League teams and getting taunted by teammates for being awkward and effeminate.
In private, she identified as female, trying on hair ties and other accessories when she was alone upstairs, taking care that her grandfather didn't know.
Roem also began playing the guitar, often practicing in the basement as an escape from her mother's stormy relationship with the man she was dating at the time.
Oliveto's daily newspaper habit sparked Roem's interest in journalism. She majored in the subject at St. Bonaventure University in western New York, and she came home to Prince William County after graduation to work as a reporter with the Gainesville Times.
Under the byline "Dan Roem," she wrote about residents' frustrations with new development and Prince William County politics, mastering the details of public policy and observing Marshall — whose district she lived in — as he repeatedly pushed legislation that sought to restrict LGBT rights.
Roem also joined the local death-metal music scene, co-founding a band called Cab Ride Home whose hard-charging songs contrast with the quiet suburban persona she has presented on the campaign trail.
In 2012, Roem began her physical gender transition. Three years later, she legally changed her first name to "Danica." Her byline changed too.
Then state legislation targeting the LGBT community, including two bills sponsored by Marshall, prompted Roem to drive to Richmond to testify in opposition. Her days as an impartial observer were over.
When some Democratic Party acquaintances suggested she run for office, she tapped into savings meant for a new house and began campaigning full time. She out-hustled three primary opponents to capture the nomination in June.
Her mother, beaming, said Oliveto would have been thrilled to see his grandchild's name on the primary ballot. The candidate wasn't so sure.
"I said: 'Ma, I don't know if he'd be proud,' " Roem recalled, her voice cracking with emotion as she gestured to her black dress and trademark rainbow scarf. "Because, he wouldn't be proud of this. I don't know how he'd ever reconcile the idea that his grandkid is transgender, and his grandchild is running for office as a trans woman."
Rainbow scarf and Route 28
Virginia's 13th District still includes plenty of social conservatives. Voters there have elected Marshall 13 times, going back to 1991.
But the area is also changing demographically, and Roem campaigns accordingly, alternately highlighting her transgender identity and playing down its significance to focus on traffic, crowded schools and aging business strips.
She dons the rainbow scarf while canvassing for votes, refers to herself in campaign literature as a stepmom to her boyfriend's 9-year-old daughter, and jokingly complains about the pain of being on her feet for extended periods while wearing high heels.
Her flirtation with history has helped her rake in nearly $500,000 so far, mostly from outside Virginia, with a big chunk coming from millionaire Chris Abele — a Milwaukee County executive who also chairs the Gay & Lesbian Victory Fund.
Marshall balks at the attention his opponent has received and openly questions her trans identity, while his supporters mock her musical pursuits.
The incumbent also calls Roem disingenuous because she broke an early vow to keep individual donations to $500 or less — a promise Roem now says was naive in light of what it takes to run a successful campaign.
"He did not keep his word to himself," said Marshall, who has also relied on large donations from individual donors.
Roem, meanwhile, accuses Marshall of being ineffective and too focused on social issues at the expense of passing legislation to help his district.
She has proposed using $300 million in state funds to build above-grade bypasses at several intersections on Route 28, eliminating the need for traffic lights. The money would be diverted from an already-funded project to build a new intersection at Route 28 and Interstate 66, which Roem argues should be paid for by the private company that would benefit from planned tolls on I-66.
Martin Nohe, who chairs the Northern Virginia Transportation Authority, said Roem's plan would help some but isn't the best long-term fix because it wouldn't add more capacity to the narrow portion of Route 28 that runs through Manassas and Manassas Park.
Nohe also said a short-term solution proposed by Marshall — reversible lanes on the highway during rush hours — would lead to bottleneck congestion where those lanes would end.
Roem has struck a chord by focusing on the roadway, Nohe said, calling the traffic problem "by far the number one issue with voters."
"No opponent of Bob Marshall's has ever gotten this level of attention," said Nohe, who in addition to his post with the transportation authority has served as a Republican supervisor in Prince William County since 2003.
Taking center stage
The McMansions and cul-de-sac streets of the Heritage Hunt retirement community in Gainesville are Marshall country. Roem stopped at a supporter's house for wine and pastries one recent day, hoping to steal a few votes.
Addressing about 30 senior citizens in the living room, she joked about being "an Italian extroverted woman" before launching into yet another set of treatises on Route 28; the need to extend the commuter rail to the Innovation Park business incubator in Manassas to lure more high-paying jobs; and eliminating local taxes on business and professional licenses.
When she was done, Roem pointed out she had not mentioned anything about LGBT rights.
"I really want to drive home the point that I know the public policy issues of the 13th District," she said to applause. "This is what I focused on as a reporter, and this is what I will focus on as your delegate."
Collin Robinson, 70, went out to his car to retrieve his checkbook, then donated $500 to Roem's campaign.
He said he usually votes for Democrats but backed someone else in the primary because of Roem's transgender status.
"I was afraid Northern Virginia couldn't handle an LGBT candidate," Robinson said. But after seeing her in person, he decided she was "very believable."
On another day, Roem headed to Washington, where Arcade Fire, the Grammy Award-winning indie rock group, was headlining a rally on her behalf.
The audience was a mixture of LGBT supporters, campaign volunteers and 20-somethings who were mainly there for the band.
Lead singer Win Butler praised Roem as an example of "trying to build the community and the city and the state and the nation that we think reflects who we are."
Then Roem took center stage, clutching the microphone with both hands as if she were about to launch into a blistering Cab Ride Home number.
Instead, out came a small, heartfelt speech about chasing your dreams.
"You can succeed because of who you are, not despite it," Roem said. "You can succeed because of who you are, not for what other people tell you you're supposed to be."
Roem left the club just past 1 a.m. A nearly traffic-free Route 28 greeted her on the way home.