I agree with pauliew, Teresa has real potential. Every soap needs at least one character who is entertaining and irritating in equal measures. I think Teresa provides a sort of 'safety valve' for the rest of us - she behaves so naughtily and selfishly that it's almost like she's doing it for everyone else watching who would never dare behave so outrageously. It's also comforting for most people to know that there is at least one person out there who is more self-centred, greedy, cheeky, grasping and thoughtless than they are!
So, keep the old cow in, I say. We need a truly awful (but fun) female character. And consider the alternative: if the mighty T leaves they might resurrect Jackie! Agh! Please! Never let her darken the cobbles again with her overt 'I'm a Scouser'-ness, dreadful posturings and primary school thespian skills.