I'm going to make my sister give me the hockey puck that she caught
Is there a reason you won't let her keep it?
I've decided I want to keep it and I don't want to share.
You should not demand things are not yours. She caught the puck, so it is hers to keep or to give away as she pleases.
Fuck you and her.
I'm sorry that this upsets you, but it is only right to let your sister keep what is rightfully hers. You have no claim on her property because she was the one who caught it.