Hello there,
I am not an expert of psychology but I know a thing or two about depression. Yup, because I have suffered from this and still am but on the way of recovery. Anyway, the problem you are having is really very common with the people who have depression.

When a person have depression, it's like the will to be emotionally invested in something dies within. Nothing can do can make them feel better if they don't want to. She definitely loves you but her state of mind is stooping her from feeling this. She tried to break up with you probably because she wants to be alone. My advise would be, let her be for sometimes. I am not saying you should leave her alone, just stop talking about her situation and asking her how she feel. These are the worst things to say to a depressive person. Instead tell her, "I care for you and no matter how much time you need, if you want to share your problems with me, I'm here."
This phase is like a perfect balance of consolation and also not being pushy. She will know that she has someone to go to when she is ready. I hope this helps. All the best to you and your partner.