Screener moving backwards

[Paul in Seattle]

Folks,

Can't find a specific rule/casebook (NFHS) situation to back me up here. But in my ballgame the other day, B1 didn't like how A1 was setting her screens. A1 is well in front of A2 (who has the ball), facing away from her (both A1 and A2 are facing the goal). B1 tries to get to the shooter, and as she does, A1 backs up towards A2. So we have A1 and B1 moving the same direction. I nail B1 with a foul for escorting A1 along with a forearm push. B1 (the captain) says "she's moving on the screen." But this movement--backwards, in the same direction as B1, is legal. Ain't it? I can't seem to find a good rule or casebook moment on this...can you?

Paul