Any believable reasons why Pansy might join Harry’s side?

Emphasis on believable. I’m kicking around the idea of doing a Pansy fic, but I’m struggling to nail down her motivation. Self-preservation seems in character, but I’d like there to be something deeper beneath the surface. For example, I think The Truth is Stranger had her with a squib sister she wanted to protect, which I thought worked well.

My idea would have the story start sixth year, but since I recently did a Horcrux/Voldemort fic, I’m also debating skimming over that part and letting the main part of the story be about post-war reconstruction.

Any thoughts would be welcome, cheers.

Edit: Thanks for all the input. After going through the replies I wrote like a 2 page manifesto on why Pansy is the way she is, and why she ultimately decides to switch sides. Hopefully the rest of the fic comes together, but thanks again for the help.