Can you talk to another ref for that level?
I'm a firm believer that even juniors should be told ALL the rules & have them explained.
If you think someone is deliberately intimidating a player then call intimidation and explain what it is.

Otherwise if you notice it chat to the coach at 1/4 time and say your GK is intimidating people (specific example if staring or pulling faces).
Ask they discuss it with her and if it continues you will call her on it & give away the free pass.