'It is the bad ones that give the good ones a bad name.'
^^^ I agree and it's the same for many professions. Just don't let this one person tarnish your view of all of them, most of them do care and also do a job that I wouldn't even consider for not great money. Two members of my close family are carers, they'd not be very impressed with your aunts experience of this carer. That's why a complaint should be made, either the carer needs some basic cookery lessons or the whole matter needs investigating properly to make sure the carer is cutting corners in other peoples homes.
I used to manage a carers in the community thing along time a go specifically for elderly who just come out of hospital and needed help. I would have expected to be told about any incident like this.