It's only human to feel guilt (it means you likely also have empathy for others which is a good thing). From what I'm hearing here, it sounds like you feel bad because you feel undeserving of but also lucky for landing the role/team. But there are just so many factors that only you would be able to assess (e.g. is the guilt coming from you internally only or is it also externally from her and the way she talks to you is meant to cause you guilt).

Nonetheless, it sounds like your coworker is in an unhealthy environment that is outside of your control. You may feel like you were the indirect cause of her misery but remember you were/are not the direct cause of. It's something she needs to consider herself and find a solution to as well, especially if she has chosen to stay in this role for two years. Just my thoughts.