Hi! I'm a green card holder, can I petition my girlfriend who got a working visa after marriage?
Or do I need to be a US citizen before I marry her so I ca petition her? Please I need your reply. Thanks.

It takes longer time for spouse of green card holder to get visa number. If she has proper visa that allow her to wait for immigrant visa that long, it's OK. If not, you should wait until you become naturalized, it will take only a few months.