Syncing issues

[Jamer]

I have an iPad 1 that I use for work, I sync everything on it with iTunes. Now here is the question, my girlfriend has an iPhone but when I logged into her Apple ID on my iTunes and synced everything was fine until I pluggs my iPad back in, it then transferred all her stuff onto my iPad? My daughter is coming home later and wants to sync her iPhone, now how do I achieve doing all this with these various devices on one computer? I was under the impression that as long as you log into iTunes using your own mac id that is how it works yes?

[Sponsors]

[JezzerP]

It works best if each of you have separate user accounts on the Mac, and separate iTunes IDs. Remembering to log on and off with different iTunes IDs on one account on the Mac can get confusing.