ignore the rumours man, most rumours are started by jealous people or bitter ex's.
make sure you wear a condom, get good condoms, not cheap ones, and if you're worried about sensation, then get sensitive ones.
also good to check if shes on the pill, condoms are only 99% effective, so thats food for thought surely?
also, if you bring up the fact that you heard a rumour she has an std, then arent you worried that she'll get pissed off and then wont have sex with you?
and do you really want to just get laid with a one night stand sorta scenario? i'm not saying i havent had my fair share of them, but i usually dont think they are worth it tbh