Democrat Elizabeth Colbert Busch's first TV ad since the primary in South Carolina's 1st congressional district is all about trying to convince voters she's an independent voice who isn't beholden to her party.

"As a single mom raising three young children, I had to be independent and do what was right for them," the Democrat says in the ad, which she released Tuesday morning. "Now, I'm going to take that lesson to Congress. I won't take any special interest pledges or follow any party line."

Job creation and deficit reduction are two other issues Colbert Busch mentions in the spot. She concludes: "My only pledge is to do what's right for you."

The campaign did not immediately disclose the size of the ad buy.

Colbert Busch, the sister of Comedy Central host Stephen Colbert, is competing in the special election in the conservative-leaning district against former Republican governor Mark Sanford. Given the strong GOP tilt of the district -- Mitt Romney won nearly six in 10 votes there -- Colbert Busch has been underscoring a campaign message consistent with her new ad; she's been describing herself as an independent voice.

Whether it works or not remains to be seen in the coming weeks. Republicans, meanwhile, are casting her as a liberal who is out of touch with the fiscally conservative sentiment of the district. They note that she has accepted money from labor unions and is raising money with liberal members of Congress.

The special general election will be held on May 7.

Updated at 11:59 a.m.