How to turn off I cloud sharing from my iphone to another computer?

My sister just got a new mac book and the new os lets her see my messages, i've turned it off before but her computer has a lock on it, can I turn it off from my my phone somehow?

Why would you want to? 800 dollar for a personal tracking machine.

I don't want my sister to be seeing all my messages

Sounds like you are using the same Apple ID on both devices. Getting separate ones would stop that.