It helps releive cramps, she also may be more horny from hormones. Listen to what the lady says though, dont try and force an issue. It may get messy (yes it is more of a clean up, and it stains) but who cares.
Just an opinion, but going down on a woman who has "fallen to the communists" without a tampon is kind of gross and unnecessary. Cant you just wait a couple of days? Does blood and mucus etc turn you on? If so, and your lady friend is down with it, well go ahead.
"You down with OBG? Yeah you know me!"