Hi there,
What you are describing is gaping.
This is how beardies regulate their temperatures and cool off.
If your dragon was doing this anywhere else other than her basking spot it would be an indicator that its too hot in there for her.
As she was doing it on her basking branch its likely that she was just being lazy and gaping insted of moving away from the heat.
Just to check though could you tell us your temperatures for your basking spot and cool side?
Temps should be taken with a digital thermom with a probe, anything else can be up to 15degrees off!
Holly