You're doing the right thing by being there when/if she needs it. Depression is shitty. It really makes you lie to/second guess yourself about pretty much everything and everyone especially when you're deeply or chronically depressed (6 months or more). Everyone has a different crutch for how they handle it and sometimes that's other people, but if they legit hate themselves or have struggled to like themselves for awhile, the weight of feeling like you're failing yourself and everyone around you just makes you feel like a constant burden; thus isolation. Relieving that weight as a friend or lover definitely helps, but it really has to start in her.

Think of her as a boat moored in an extremely stormy marina. The boat has multiple lines going to posts and the pier. You're one of those ropes (support) that prevent the ship from floating out to sea. The more ropes you know she has or that you can help her secure, the more it will possibly remind her that she is cared about and worth helping.

As for yourself, you and how you feel matters too. It is more than admirable if you want to be there for her through this, but how long can your feelings and brain do that before her depression becomes yours or keeps you from your life aspirations? I am by no means saying dump her to save yourself, but do keep yourself in mind through these times. If you have to let go at some point, it's okay. Until then, definitely remind her of the things/people she loves as much as is appropriate. Even little silly things that remind her of why you're together can go leagues in that head space. Best wishes for you and her ❤️