I am going to be frank with you. There are levels, levels of depression and levels of mental illness in general. No two experiences are exactly the same but there are, and will always be, levels.

For example, I have suffered from depression for as long as I can remember. However mine is more along the lines of environmental depression and learned behavior/habits. With therapy, and a strict set of rules in term of self care, diet and exercise it is now extremely manageable. I have low times every few weeks where I will do the bare minimum that I need to do but it is no longer debilitating. My SO wouldn't know how I was feeling unless I told him. I have never, not once, felt the urge to pull out my eyelashes.

Then there's depression on the level my mother suffered, her hatred of self ran so deep it was excruciating to watch, you could literally feel it across a room. She would pull out her hair frequently out of sheer frustration of not being able to get a handle on her own mind. She self medicated with alcohol starting around your girlfriends age (not saying she will). I frequently dealt with a drunk/passed out/aggressive/crying, etc mother and one day when I was very young I came home from school and she had shaved her head. Her depression and mistreatment of her body eventually led to her death, which myself and my family are still recovering from. Her illness was not something that could be treated and managed in a "mild" way like mine. It required medication and significant and consistent intervention by psychiatric professionals and that still didn't save her.

The kind of mental illness your girlfriend is experiencing is closer to my mother's level than my own. This is not to say she cannot help herself and live well, she can, many have. But she needs to do it with medical professionals, she cannot lean on you alone for this. It will crush you. You cannot save her. Do not allow yourself to be destroyed by this, you have done your best, you gave it your all and that is enough, no one can or should ask more of you. Save yourself. It is not selfish, it is necessary. It is not your responsibility to carry another human being through life. It won't help her but it will destroy you. If you're a good person, you will feel guilty and that's okay. It really is. Feel it, move on and live well. I wish you the very best.