I agree - you passed and that's already a great achievement - well done !
Now on to the not so fun stuff - it sounds like there's a tiny bit of sour grapes here - you knew you were ill, you knew the pieces didn't suit your voice etc. yet you still chose to go ahead with the exam, if you feel you haven't done as well as you deserved, then you have to acknowledge that this is due to your choice, not to anyone else.
I agree with David, though, your teacher shouldn't be forcing you to do certain pieces - you should be the one to choose with appropriate guidance - however it was your responsibility to say something before the exam rather than once you got the result.
A singing teacher does not need to be able to accompany you, either - in fact whilst accompanying you, there's a chance that they aren't able to focus all their attention on you, so a teacher who continually plays piano is not necessarily a good thing. I play the piano to a relatively high standard, but apart from warm-ups and cool downs and the odd tiny bar of accompaniment here and there, I do not accompany my students - if they want accompaniment they bring their own pianist, as for learning songs, we do it by ear from recordings or sight singing if they have the score.
Where your current teacher is concerned you've highlighted several things that you aren't happy with :
1) she doesn't play the piano well - that doesn't mean anything at all.
2) she forces certain songs on you - it's up to you to be more assertive.
3) she's slightly deaf - this could be a problem.
However, you also said that she's taught you a lot and, to be honest, there's a fair chance you wouldn't have got to grade 7 without this woman.
Rather than pointing fingers at things that are ultimately down to you, I'd try being a bit more assertive in lessons for a while and see how that goes. Get an accomanist if necessary or sing to good quality backing tracks - it's what most professional singers do.
Then if it doesn't work out, you can leave in all good conscience knowing that you're leaving because your ideals for singing have diverged, rather than pretending it's her fault that you didn't do as well as you think you ought to.
Once again - congratulations on your G7 - that's a great achievement that you should be proud of.
Allan