I believe, people come into our lives for a reason, they don't always stay and she was there when you needed someone, that's a gift.
It can be totally overwhelming, listening to so much pain, negativity that sometimes people "have" to withdraw for sanity.
You say you don't deserve her, yes you do, did, she came into your life.
A card, a simple "thank you for all you are, I needed you there and you were, keep in touch"
Is probably all you need...
It sounds as if you "need" someone still there for you as you are not coping, maybe take that off of "friends" and their shoulders that are new to you, and seek someone outside that can help you grieve.