I am kind of uncomfortable with her knowingly using her looks to get guys to buy her drinks

She's not forcing her looks on dudes. It's not like she's going out to bars and holding men down with her beauty until they buy her and her friends booze.

Men are buying her and her friends stuff, without her doing any work what so ever, just because she's pretty.

It sounds like you're more uncomfortable with the men doing this than you are your girlfriend, especially if she doesn't know she's doing it.

My advice is for you to have a talk with your friends and tell them that they shouldn't buy pretty women drinks anymore. Talk to all the guys you know, as a matter of fact. Let them know that there are boyfriends out there who really dislike the fact that their girlfriends sometimes get free things because they're pretty, and they'd like that to stop because it makes them uncomfortable.