If she is positive (we dont know), so your saliva neutralize the virus from her period blood in your mouth. Anyway, if you can not clearly bleeding wound in the mouth, the risk of transmission is zero. HIV virus must rub deeply into the mucous membrane, is not enough only contact with the virus.
In oral sex, exposure to virus carrying body fluids (semen or vaginal fluids) is mostly there but even then this mode of sex is called a zero risk activity. Same should go for blood. Therefore you need not to worry about HIV if the exposure in limited to oral sex only.
HIV transmission is possible via unprotected anal and / or vaginal sex only when we talk about sexoual routes.