What pet should i buy for my gf?

Oh Dory Dory, I don't have a clue. :-(

PS.

But thanks for the BA's bro. :-)

Never buy someone a pet without checking with them first.  A pet is a huge responsibility that a person may not be prepared for --  and also something a person needs to select on their own. So ask her if she wants a pet, and if so, take her out to select one for herself. 

Chances are pretty good she already has one in mind that she would love to have. I'd figure out a way to subtly get the information out of her so that you can get that.

It depends on what she likes and her circumstances. If you aren't sure, maybe just ask her. You can make the questions hypothetical, but make sure you know that it's what she wants because getting a pet is a pretty big deal. 

A dog or cat, find out what she likes

Low maintenance... gold fish, turtle, etc.

nothing        

I would let her choose which pet she wants seeing as she will need to care for it for many years.