I would definitely talk with her and let her know how you feel. If the female pet who had the litter is one that is to be "off limits" and not in the mix to share, then your mom should have made that clear to you then you wouldn't feel as you do now. In my opinion, if this particular furbaby is not to be in the loop and you were not aware before the litter was whelped, then to make things right, your mom should split this litter with you but no future ones if another accident occurs. That way, there is no hard feelings between either of you. Best of luck to you