I am a hobby baker, so not dependent upon cakes for a livelihood. If someone started out by complaining about my price, I would shut down negotiations right then and there. It would go no further and if she ever called again, I would tell her I was completely booked. This was an accident just waiting to happen.
You were more than generous and extremely patient and should definitely not have offered any refund. Unfortunately, nothing you can do about the hateful comments except delete them from your page.
Sugar Sugar by SSmiley