I like to think of Sylphs as players who guide and nurture using their Aspect. So a Sylph of Blood would probably be quite similar to a Maid of the same aspect. She’d keep an eye on her teammates and try to make sure they’re all getting along, while perhaps steering them away from alliances and relationships she deems unhealthy. She could even pacify or make alliances with unlikely individuals - the Blood player is probably always the one you want to send to get Jack Noir or a similar entity on your side. She might also use her aspect as leverage. Perhaps she’s very good at making people think she’s their best friend, charming them into doing whatever she wants. She wouldn’t force people to do anything. They’d be falling over themselves in an attempt to please her because she’s just that great!
Of course, that can be dangerous. As I’ve said, Sylphs seem to lean either too passive or too active. While a passive Sylph fears to interfere in messy team squabbles, an overly active one might try to manipulate them or use her position of power to make people do what she thinks is best. Being a dictator - even a well loved one - is no good.
Of course, there’s more to the Blood aspect that we don’t know yet, so unfortunately this is all I can tell you. For now.