Is it okay to tell my girlfriend that she needs to shave her legs?
Why do you want your girlfriend to shave her legs?
I read this survey that women with hairy legs are noticed by other people.
If hairy legs makes you uncomfortable then you should bring it up with her. If she doesn't agree, then you have to decide which is more important.
I'm going to tell her today.
Ultimately it is her body, but as her boyfriend you can give her friendly suggestions as to your preference. Relationships are all about compromises, so see if you both can arrive at one.