Why did my photos get transferred to my moms phone?

Okay, my mom got a new iphone 7, and when she was transferring her photos from her old phone to her new phone, all my photos from my Samsung ended up on her phone. Why did this happen and how do i prevent this from happening again?

Buy your own phone, with a separate plan.

You could be sharing the same iCloud account so if you take a picture it goes to the cloud and the cloud is accessible on her phone. Make a new iCloud account. It's free

You she an ID? IF so that is why

I'm going to guess it was something to do with some photo sharing service that you'll may be using & sending them across both devices. I'd go back over that to see if there were any issues.

Don't see how otherwise an iPhone 7 would suddenly get pictures from a Samsung phone.