Welcome here to the forum, a good move as others may well have had similar experiences, plus in your position having support makes a difference.
I think you are very wist to start drawing boundaries and trying to limit your help. Yes, this person is your friend, however I suspect you are not dealing with one person who has depression, but two people, one of whom is making life less tolerable for the other.
Reading you post the bit that jumps out at me is as follows:
"her partner always enforces their needs over hers. When I say she’s
given up it’s like she’s succumb to living the life the partner wants
even if it’s not quite what she wants, and that’s resulted in my friend
being absent, anxious, sleep deprived etc"
Now without knowing all the facts maybe I'm giving this too much significance however there are people that live in an abusive relationship. One partner tries to control and dominate the other. Insisting what they want is the important thing and the other person's wants ignored. It goes further than this in lots of ways including isolating the person by discouraging friendships and family contact.
Should that be the case it has a very marked effect on the mental health of the person being abused and they can indeed decline and simply do 'as told'.
So I guess I'm asking you, in view of what I've said, is this likely to be the case -after all you are the one with a closer knowledge of the circumstances.
Should you feel there is a chance that the sort of behavior I have described is possible may I suggest you give the experts in such matters, 1800Respect - 1800 737 732 a ring and seek their advice. It's free and they are sensible and knowledgeable.
Please let us know how you are gettng on