If two iPhones are synced what all do you see from the other phone?

I have one my best friend gave me because she just got a newer iphone. They are currently synced and I'm in the process of saving the photos to a computer before setting up a new iCloud account. I'm curious what can my friend see besides pictures I take? I'm new to iPhones and I don't want to overload her gallery with pictures I've taken already. Any information you can give please share, thanks so much.

She can see whatever is synced with the cloud: email, photos, texts, notes, etc., depending on phone settings.