Hi Ybas, welcome to the forum
You are never overreacting if something bothers you. You should tell your husband about it and kindly request him to take into consideration that this bothers you. I must say however that perhaps the girl genuinely likes your husband and it is not her fault that her mom and he broke up so why should she have to suffer from what grown-ups have decided? It cannot be easy on a child (and later teenager or adult) to 'discard' someone that had a specific role in your life just like that...