She may be wearing the garb of the church but this lady is definitely another reaver! Keeping Tryxxie locked up as a ready source of essence to snack on. So much essence gone that Tryxxie forgot herself.
Heck, most, if not all, of the monsters we fought in the Overthere were souls that had lost themselves over the years or centuries. Not all turned into reavers, but the reavers were the troublesome ones.