How to disable my messages from going to another iPhone?

So my mom got this new work phone and basically she can read all of my messages which makes me very uncomfortable because I'm a 16 year old with a boyfriend and a social life and really don't need my mom watching my every move. I know that If I go on her phone I can turn it off but there has to be some way to turn it off on my phone too.

Only send messages that are appropriate for anyone to read. This way you won't get into trouble.
Remember that anything you say or do on a cell phone or online will be saved forever. A picture that you meant only for one person to view can be passed around to everyone you know in a matter of minutes.