It can be both. She deserves boundaries, and she deserves context.

It’s not an excuse, it’s a reason. That doesn’t mean it’s okay, and you absolutely need to find external help and other people to lean on.

You’re right, it’s not fair to make one person feel guilty or responsible for your mental health, but it’s equally not fair to you- you need and deserve a whole team on your side.

Glad you liked the ‘lifeboat’ idea. It’s simple, but it really does work. Do that small thing for yourself, then do something bigger- ask for help. If you’re in education there will be a whole raft of services available to you. Use them! Get your money’s worth!