It’s fine. It’s not required that she be a Catholic.
You also don’t have to wait till your mom is passed away to pray for her, it would be good if you did it right now. Most parishes have lists to pray for the sick. If it would upset your mom to have her name in the church bulletin (I’m thinking if she’s 94, unwell and doesn’t attend your church, she might not know her name is in there) then you might want to ask if they could just put it as “Special Intention”.
If you wanted to have a Mass said for her right now while she is alive, you might want to use one of the many online sites where you request such a Mass from priests serving in the missions - your Mass stipend goes to help the missions. If they send an acknowledgment card, you can ask them to please send it to you yourself so again your mom wouldn’t know about it.