Jeeze, why all the squeemishness? I love it! I can't think of a more intimate act. And there is nothing inherently unhealthy about eating some of her period blood. Sure it passes through her vagina, but I love putting my tongue up there when she's not bleeding, so what's the difference? Sex is not, and should never be considered, "sterile". You're sharing body fluids. I love her juices. And I'm a PhD microbiologist.
It's not waste, either! It's the discharge of her moontime, the energy she has expended to prepare her womb for conception. If you're a woman and your man won't go down on you during your period, you don't know what you're missing out on. The orgasms can be the most intense you've ever experienced because your hormones are in a state where you are sexually primed for spectacular release.
And if you're a man, man up! Her ***** is prime at the beginning of her cycle.