Thanks for the responses and the casebook reference... turns out I was looking at the wrong sections of the casebook (Rule 10 instead of Rule 4).
RE: Telling the player that she needed to stay on the spot... believe me, that thought occurred to me immediately after the smoke cleared. And I'm going to start doing that from now on.
Other context:
Before the game, the Team A head coach offered to grab a whistle and act as the second official.
"Coach, I appreciate the offer, but I can't let you do that for several reasons."
I found out after the game that the Team A head coach is A15's father.
Should've been an interesting ride home, to say the least. I can only hope it was a productive "there are consequences to unsporting behavior" type conversation rather than an "officials suck" conversation.
This was the 5th of 6 games I worked solo that day. The 6th game was worse in some respects... 1 unsporting player T, 1 unsporting coach T, and a "Worst Official in the World" award handed out after the game by a fan standing at the exit of the gym.