Hmm, agree with all the above, she could have a phobia, it could have been impossible with childcare etc, but surely she would have said that?
TBH, if you truly valued your friendship and don't want to lose it, then you are going to have to have a very gentle sit down with her.
Along the lines of I know you said you were busy, but it really hurt that you didn't try and visit me. I'm sure you didn't intend that to happen, but I need to tell you how it made me feel.
I was hospital phobic and did faint at the merest whiff of their disinfectant smell, before DS was born. Now I think I'm OK, can just about handle a short period of time without bursting into tears, throwing up, passing out or a combination of all three...
If you were my BF, and if I thought I couldn't handle it, I'd tell you I just can't visit in hospital and why, if it were a childcare issue again I'd tell you and in both cases, I'd make damned sure I was there for you when you got out.
Simply saying I've been too busy to wipe my own arse is not a good enough excuse imho.