Rovosangue

A legendary permanent that is put into a graveyard because of the “legend rule” isn't sacrificed.

Bloodbriar's ability is a triggered ability, not an activated ability. It doesn't allow you to sacrifice a permanent whenever you want; rather, you need some other way of sacrificing permanents.

If you sacrifice a permanent as part of casting a spell or activating an ability, Bloodbriar's ability will resolve before that spell or ability.