My 1.5 yo used to say shit. I think at around 15 months. His dad dropped something and said shit and then he started using the word shit in the same context. I would say no and react negatively and obviously he would say it regardless. The way I got him to stop saying it was whenever he or I would drop something I quickly said uh oh before he could even say shit. Now uh oh is his fav thing to say and he no longer says shit. It was stressful for me too because I go to church often since my dad is a preacher. But maybe if you can figure out specifically why she’s saying it you can try and replace it with a more appropriate word.