If it's been part of your conditioning- or just part of your nature/personality- to try and help people, fix situations, make them feel better by taking the blame, rescuing them, etc--- those things you are feeling can be pretty hardwired into the system.

Honestly, it's always okay to feel compassion for other people, no matter the circumstances. Healthy boundaries can keep us from going too far with that compassion. You can feel it without giving away your power, time, or energy.

This is JMO, but I think the longer the situation goes on with a disordered person, the more pointless and futile it seems, the more you realize that there's not much productive coming from their end, and probably never will be. You start to get over those feelings a little bit more.

Remember what they say: you only get to take responsibility for 50% of the relationship. What did she do to meet you in the middle?