Essie is equally intimidated by Sy, especially after he got mad at her list. (She was definitely NOT thinking about him kiiinda being her cousin when she made the initial list, WHOOPS.)
The fact that Sy DOES lighten up a little is certainly cause for speculation, though considerably more somber than at the earlier Ebonhide practice.
(Essie has no idea about Reid's supernatural status, but she probably HAS seen Mina's prom photos on more than one occasion. Of course vampire lore is so varied those can hardly serve as definitive evidence.)