If a parent has full custody and decision making that means they make all decisions including what religion the child practices. Let's say mom is Catholic and dad is Jewish. Mom has full custody. Child is 16 and child decides they want to convert to Judaism. Can mom stop it?

Update: So I'm the girlfriend in this story. My boyfriend's son has always wanted to go more towards Jewish faith my boyfriend's son is antisemitic. He was actually supposed have a bar mitzvah but she made him miss it. So pretty much he's been acting up in church since she is trying to stop him from converting to Judaism. He is embarrassing her bad and she says she's gonna take us to court over this but what is a judge gonna tell a 16 year old. No you can't worship the religion you want? Isn't that a basic right?