First, how she isn't wearing a nun outfit.
Second the fact her hair are clearly showing, probably on purpose from the author.
Third, Sharon's journal was mentioning TWO women in white sister habits (chap 60, p.4), Daleth said during sabbath she barely knew Sharon but knew who was the witch who cursed the duke and despised her (chap 39).
Fourth, the assets, if you catch my drift, as shown in chap 40 and 61, Dulles/Daleth (?) is quite busty, though it also goes against this masked person being Alice I guess.
Some options being : she's the same white nun we know (she knows about the journal), she's someone unrelated maybe the second white nun, she's Alice from the future but if Zain is the one controlling time that's unlikely + lack of cleavage, she's Sharon, she's the witch who cursed the duke which could incidentally be any of the aforementioned.