She needs to get treatment, for her sake. Ignoring your craving for sex completely, she needs to get proper help. The priority should be making sure she is as well and safe as possible, living as good a life as possible. Bonus would be that it helps your sex life too, of course...
Making any conversation regarding her depression about your sexual satisfaction is unlikely to end well. You need to make any conversation with her about her depression about her getting well for her sake. Making it about your sexual satisfaction may run the risk of her thinking you care more about that than about the fact she's currently internally suffering and sick, you know... not that it's wrong for this to be an issue for you and for you to feel this way! You're human too and have your own struggles. It's just it wont help giving her any sort of reason to think sex is more important than her as a person. Mental illness has a wonderful way of warping things for the worst.
Talk to her if there's anything with sex she wants to try and feels more comfortable doing. Don't talk about her depression or how it's affecting your sex life - but you can spark up a conversation about sex on it's own, without mentioning the depression or that she's somehow at fault. There may actually be things shes still wanting to do, or will get satisfaction from. You can at least make moves to find out, if you havn't already? Or think up some new things yourself, and ask her if she would like to try (gently, with no pressure).
But of course you need to get this sorted properly so you're not having to tip toe around this, and she can feel better, and so you can too. It's unlikely she will be able to pull herself out of depression on her own, unless any of her depression is situational and that situation changes/she can work through it. Perhaps ask her about that, if there are any situations contributing to her depression that you can work together to fix... but ultimately, yeah, the aim would be getting her proper help.
If this never resolves, and no matter how hard you try she wont agree to make moves to get help or make changes to feel better, then I would say you need to consider other options. There may come a time you need to be harsher about it than the softly-softly approach I am suggesting... open relationships, breaking up even... It's not a nice thought, but you only get one life too. You matter too. You shouldn't spend life in any way miserable if you can help it either.