No riselia is not a reencarnation of Roselia is de vampire queen, the theory that MAL seiken Gakuin that we have talked about says that Tessera could be the reincarnation of Roselia, since they look quite similar and have a similar aura. In the Japanese version of Wikipedia, Seiken Gakuin says that Roselia was reincarnated as a little girl after passing 1000 years, although it is not yet specified who she is. We are waiting for them to say it in the remaining 6 episodes, in the final episode or in a 2 season.