"Will you act on your word to reject fossil-fuel money in the future in your campaign?" Resnick-Day asked after thanking Clinton for addressing climate change in her campaign.
Apparently peeved, Clinton fired back flashing a frustration that had begun to show earlier in the rally when a large group of Sanders supporters interrupted her speech.
"I have money from people who work for fossil-fuel companies," Clinton said.
As Resnick-Day tried to respond, Clinton interrupted her pointing her finger for emphasis: "I am so sick -- I am so sick of the Sanders campaign lying about me."
"I'm sick of it," she added before moving on to shake another hand.
Hillary Clinton on the campaign trail
The Sanders campaign has said that they will hammer Clinton for her ties to the fossil-fuel industry through campaign donations.
And Greenpeace, a progressive environmental organization, released a recent report showing that Clinton had also received more than $1.2 million in donations bundled -- or fundraised -- by lobbyists for fossil-fuel industry on her behalf. The organization also tied millions more donations tied to the fossil-fuel industry to the super PAC supporting Clinton, Priorities USA Action.
She has not accepted any direct contributions from oil and gas companies.
But Resnick-Day said in an interview with The Washington Post that she has no ties to the Sanders campaign and has not committed to any candidate in the race. She and other Greenpeace activists have confronted Clinton several times on the rope line with the same question in the past.
"I think that she has been annoyed to continually be asked the question on the trail and didn’t really want have to deal with the question again," the 26-year-old activist from Pittsburgh said. "I was upset that she felt that I was a Bernie campaigner, because I’m not."
"I didn’t like that assumption," she added.
Resnick-Day said Greenpeace has asked all of the presidential candidates to sign a pledge to reject money from the fossil-fuel industry and to pursue campaign finance reform. Sanders has signed the pledge but Clinton has not.
But Clinton's tone didn't really bother her as much as her continued reluctance to sign the pledge, Resnick-Day said.
"The tone at which a candidate talks to me is not what matters to me, it's the substance of what the candidate is saying," she said. "And I'd love to see Hillary come out and take the pledge to reject fossil-fuel money, especially if she's saying she did not take any, there's no reason that she can't sign the pledge."
And another incident may have contributed to Clinton's mood. Earlier in the rally, a large group of chanting Sanders supporters interrupted Clinton's remarks and walked out prompting Clinton to fire back at them from the podium.
"As they're leaving, I just want to say I have earned over 9 million votes in this election," Clinton said, adding that she has received more than 2 million more votes than Sanders. "What I regret is they don’t want to listen to anybody else."
"What I regret is that they don’t want to hear the contrast between my experience, my plans, my vision, what I know I can get done and what my opponent is promising," she added.
In a statement, Clinton spokesman Nick Merrill said that Clinton has a "proven record" of combating climate change and fighting against fossil-fuel interests.
Merrill noted that she has released clean-energy proposals as a candidate and has called for eliminating tax breaks for oil and gas companies.
"The simple truth is that this campaign has not taken a dollar from oil and gas industry PACs or corporations," Merrill said. "The simple fact is that the Sanders campaign is misleading voters with their attacks.
"The money in question is from individuals who work for these companies," he added, noting that by the same metric, Sanders has received more than $50,000 from employees of oil and gas companies.
Merrill continued: "Assuming they don’t believe their own candidate is bought by the fossil fuel industry, they should stop the false attacks and do what they’ve claimed the campaign is about: debating the issues.”
But the Sanders campaign isn't backing down.
Michael Briggs, a spokesman for Sanders, said that Clinton's campaign has relied "heavily" on money from lobbyists working for the oil, gas and coal industries.
“It’s no wonder that back in December Clinton refused to agree to stop accepting money from the fossil fuel industry when pressed at a town hall, saying, 'I’m not going to do a litmus test on them,'" Briggs said in a statement. "If Secretary Clinton wants to discuss this and other important issues she should stop stalling and agree to a debate in New York before the April 19 primary election."
The Clinton and Sanders campaigns have been deadlocked over the issue of a debate that the Sanders campaign has pushed to be held in Brooklyn, N.Y., ahead of the state's primary.