Yes, she’s LDS.
I too have siblings who are not members of the church. There are “mixed marriages” so to speak in my own family.
My son’s best friend is Catholic, and they play together nearly every day, usually at their house. I’m not sure what all the hubbub is about associating with those not of our faith. Christ never taught this, and most Mormons I know don’t act like that. Sure, there are some, but still...
I think it depends on how you interpret the religion. I’ve known Catholics who shunned divorced family members or family who married divorcees. My own family whispered about one of the in-laws being a secret Jew.
I have found that Mormons condemn kids leaving the church and heap more heavily on them for joining another church. Unfortunately I’m seeing that first hand these days. Protestant churches will sometimes engage in this behavior so it isn’t just Mormons.