Do i confront my sister about the money she never paid back, or let it go for peace?

2years ago I lent my sister R15,000 for a deposit on her flat. She said she'd pay it back in 6 months or so. She's never mentioned it again, and every time I bring it up gently she changes the subject. Meanwhile she's just came back from a girls weekend away with her friends. My mom says family isn't a loan shark and I should let it go for the sake of peace and being a good religious family. Is she right, or am I allowed to actually want my money back?