My sister says she has a religion she said she can't tell anyone do you know what religion she has?

This sounds very suspicious. Why belong to a religion that you can't tell anyone about?

If you love God then you will want everyone to know and to tell others about him. I am proud of my religion and look to every opportunity to talk about my God.

She sounds as if she is ashamed of what she worships. Has she told you about it? have you asked?

Normally if someone does not talk about their religion is could be a cult, and these are dangerous!