Yeah, the "I'm sorry" seemed appropriate. There was a situation with a customer that was not going well, and it delayed the ability of another customer to get service. Sure. Totally appropriate to apologize for the wait to me.
But to blame it on him entirely, and on his deafness, as if I needed this explained to me somehow for some reason?! Yeah. No. Bad. It would have been more appropriate to say, "I'm sorry for the delay. May I help you?"
You're right, though. Not only was she young, she also seemed like a new employee, so she probably was panicking as she was trying to handle a problematic communication barrier as well as learning how to run the register and stuff. Her behavior seems understandable, certainly. It's still inappropriate.
The thing about the lights and the yelling was just another thing that seemed to indicate to me that they didn't get what they were doing or how to deal with deaf/hoh folks.