she'll lie quietly for a while before she cries
She likely lays quietly for roughly the same amount of time each morning before calling the alert. If you take times for the alert you will be getting very close to the same A each day even if she has been awake longer.
My DS was the same, too quiet to wake me, then alert level 1 sounds (I'm awake) which I left him to do alone as I was trying to encourage him to sleep longer in the mornings but this is when I woke and checked the time, counting A from here. Then alert level 2 (hey I've finished playing with my hands come and get me up) and I would respond and get him up. Please note, no crying, no alert level 3 (where the beep are you?).
I think you'll find the vast majority of BWers do the same.