So sorry for your loss. I think just go comfortably with what your body is telling you - you dread talking to her, but aren’t sure why. So do what is right for you and look after yourself, your health and wellbeing.
As Avitorl suggests above, just say you aren’t up to it at the moment and give yourself some space. (If well-intentioned people ring, you can ease the mental load by letting it go to voicemail, deal in your own time, when you feel resilient, and you can reply by email for example “thanks, I appreciate you calling, I am not up to chatting just now, hope you understand”
I can’t articulate very well, but went through exactly that with some friends, perhaps at a deep subconscious level, feelings of resentment.(that she didn’t take that one chance to come and see your husband?). She might have been frightened, we all do things we later regret.
You might find (as did I) that many new closer friendships are formed from the most unexpected of sources, people reaching out to you that just “get it” and know when to be there for you and when you need space.