I want to be a better friend to someone struggling with mental health.

After revisiting some old messages I've realized how much of a shit friend I've been towards my friend who's been a battling mental health crisis for years. I've gotten frustrated with her for feeling hopeless about improving her mental health. I've gotten angry at her for getting snappish or verbally lashing out while in an emotionally volatile state. I tell her that I understand that she means no harm and she's just experiencing a moment of weakness, and I do but yet I still find myself reacting to it emotionally ang getting upset. She doesn't want me involving myself in her battle towards better mental health because she's worried that I'll get fed up with her and leave but if I don't involve myself she wont try to do anything for herself. There's no one else in her life who's very interested or concerned with her health and well being, which includes her. She doesn't believe her mental health problems matter and isn't very active in trying to fix them though she does acknowledge that they exist. The reason I read through our old messages today was after she told me how she doesn't want me involving myself in her mental health anymore because she was worried that I'll get fed up with her hopelessness and self pity. I was looking for old messages to bring up and use as examples of how I'd never do such a thing.

My heart sank and my gut wrenched as I spent hours going back through years worth of messages. I was specifically seeking out the conversations related to her mental health. In a good portion of them the situation repeated itself. I tried offering some sort of help related to a problem she's been facing. She's mostly unreceptive to the advice. I get frustrated with her for not putting in any effort. Some of the times I lectured her about how she wont get anywhere just being sorry for herself. I felt like an absolute POS reading the things I'd said to her. I felt even worse because of how she never blamed me or got upset with me. She always took all the blame onto her own back and felt like an even worse person. I just want to start doing and being better for her.