Hi there. I do not think that it is possible to remove or change favorite features from your email list through your ipad. I have tried this and was only able to do it on my PC. Sorry, if anybody else has suggestions-perhaps they can give you other options.
However, your ipad remembers the contacts you use frequently and will autofill their contact name. Hopefully, by you not using this person's contact--he/she will eventually drop off and you will not have to worry about it anymore.
Another thought is to use a friend's laptop and access your email to delete/change favorite feature. Good luck.