Relative has gone into isolation

Hi, I have a sister who has recently found her faith which is great! However she has now isolated herself completely from us (her immediate family) and even going as far to not let us see her children (my nieces and nephew). She has also cut off all her friends saying she needs to put God first which is in the scripture so that’s fine. She says some other things about being a “chosen one” which I don’t understand and she has some mentor in the US … giving me slight cult vibes

I guess my questions are can you not put God first and spend time with your family? Should I be worried? Or is this just what Christianity is?