I don't see her as having redeemed herself; rather, she wasn't truly committed to the pah-wraiths' goal. She was jealous and power-hungry, not omnicidal. I see her as having blindly followed a path of petty vengeance and self-satisfaction (once Dukat identified her ethical shortcomings and was able to manipulate and stoke them), became consumed in her own desire for what she selfishly thought was her due, and then turned when she saw what was really going on - which was that the pah-wraiths had no agenda other than burning things. I don't think she identified her shortcomings and repented; rather, her goals and motives were centred on her desire to get what she thought was hers by right, not omnicidal mayhem or anything related, at least not for its own sake. Once she realized she'd been "had", and the truth of her relationship with the pah-wraiths was revealed to her, she had no motive to help them and was prepared to fight to keep them locked in. It's neither redemption nor insignificant -it just shows that Winn has actual motives and her villainous actions work in accordance with those motives. If the pah-wraiths had been honest in their promises to her, I'm sure she would have convinced herself that whatever happened was rightous and worth it, but they weren't, and so she's able to see the pah-wraiths in similar terms to Sisko and she turns on them.
Do I think Winn realized she'd made a massive mistake? Yes, definitely. Do I think she truly repented her actions? Well, when her primary weaknesses (jealousy, self-rightous entitlement and lust for power) are taken out of consideration - as they clearly are when the pah-wraiths reveal she's nothing but a tool to them - Winn is as capable of doing right as anyone. As we saw in her last scene with Kira, Winn doesn't understand that her desire for power is a problem - she has wanted to be a better person in the past, but can't confront her flaws due to a sense of self-rightousness. I doubt Winn truly changed in those moments in the Fire Caves...though had she lived, I like to think that her experiences might finally have opened her eyes and allowed her to seek redemption from then on.
Basically, I don't think redemption comes with "doing the right thing" or helping save the day, but through self-reflection and self-discovery, often painful. As the Narns say, "the future is all around us, waiting in moments of transition, to be born, in moments of revelation". Give Winn some moments of transition and she might have a revelation. It's a shame she died before she had the chance to try again.