John Gill Commentary Mark 14:66

"And as Peter was beneath in the court, there cometh one of the maids of the high priest;" — Mark 14:66 (ASV)

And as Peter was beneath in the palace
Not at the lower and further end of the room, but in the lower part of it; that part in which Jesus and the sanhedrim were, being upon an advanced ground, with steps ascending to it:

there cometh one of the maids of the high priest
the same that kept the door, and let him in. The Ethiopic version renders it, "a daughter of the high priest".