That's definitely a fair point. I think you're right that the mama bear came out at the word 'baggage' and the sentiment behind it. I should clarify, I don't think Emily would necessarily think of another person's child that way, and I'm sure she would care for a stepchild as any loving mother would, but I don't think it would be her first choice.
Whoever used that word was just stupid, IMO. You have to know it is going to get back to her and it's not going to go over well!