What about if men were having anal sex with her?
Actually that shouldn't make much difference, really.
The really dangerous thing is receiving anal sex from someone with AIDS.
Female-to-male HIV transmission is usually associated with the presence of ulcerative sexually transmitted infections, such as Syphilis, in the male. It's a fairly common mode of transmission in undeveloped countries.
As I understand it, the virus is transmitted through body fluids. It is usually the man providing the body fluids no matter the orifice. Don't know about saliva but it is normally blood or semen.
The way a man usually gets aids from a woman is through oral sex ( with the man doing the oral part not the woman). With a one night stand that usually doesn't happen. It is far more difficult for a man to get aids from a woman with just vaginal/anal sex then it is for a woman to contract it from a man. Oral sex will do it though, so watch out for that guys!