
Toby's blood magic has lots of uses, but the one that she'll be using most frequently is her ability to sense the balance of the blood. Or more precisely, to sense what species a person is. It's pretty subtle and most people don't know she's doing it when she does, as the only outward sign is that she opens her mouth a bit to "taste" it.
In her world, she's only used the ability on Fae, since no non-Fae supernatural creatures have shown up, but I'm going to extend it to non-Fae here. She won't know what a vampire or werewolf feel like at first, for instance, but she won't forget once she learns. I'm gonna also say that different canon creatures have a slightly different taste, though not enough to be unrecognizable.
She can also smell magic and recognize who cast a certain spell by the particular smell left. For instance, her own magic smells like copper and cut grass, while her boyfriend Tybalt's magic smells like pennyroyal and musk. Feel free to make up some sort of combination for your character!
She has other powers, too, like her ability to see a person's memories by tasting their blood, or her ability to actually change the balance of the blood, but she's very unlikely to use these abilities unless it comes up in a plot, in which case it would be better to discuss it then, as I'd need specific information in that case.
I realize that such knowledge can be pretty info moddy if not dealt with carefully, so I intend to check with other muns before having her use any abilities. To speed that along, however, I have made this handy dandy permissions post!