You are not a bad friend, SHE is... uh oh... and i'm just like her see? gosh..
Is it possible to say to her, in a nice way, that you're taking a little break now. And then just not talk to her for a while, concentrate on yourself and THEN, when you feel up to it, discuss about this with her? Maybe you could get her to realize what she is doing? With a calm, peace making tone, so she'll really listen to you. Maybe she knows about it and can't help herself? Maybe she has trouble dealing with your disease cuz you are her friend? Whatever the reason is she does this, i'm sure you'd both feel better if u had a thorough conversation about it.