To play devils advocate, Carol forgiving Janet for her behavior actually fits right in with the retcon, if we take as happening after Marcus starts exerting his mindwash on her. So the initial outburst is her actual feelings as the baby Marcus doesn't have the power to control Carol, then later when he's an adult he can start controlling her and the result is of Carol being all 'oops, my bad!'
Obviously I realise it wasn't written that way, and was just EPIC FAIL on behalf of the original writer but still. Taking the retcon into account, it makes sense, of a kind.