That's a tough one for sure.
I applaud you for wanting to figure this out rather then just cut her off completely-but pulling back will be tough. She'll immediately see it as another rejection (or whatever).
The only thing I can really say is just be honest. It will be hard-but I think if you tactfully say---i love you, I am not trying to end our friendship, but I think you depend on me a bit to much and it's not healthy for either of us. And then set the boundries or say-i can't answer your calls constantly and drop what i'm doing, etc...so please don't be offended if I don't call you back right away, blah, blah.
My guess is initially she will be hurt and sad, but will either come around, (and may be stronger for it), or cut you off for a bit out of hurt, but let her have her space then and don't push it.