The fact you can't take food is tough, I have heard of it at some places. DS2 was at private clinic that had a few different specialists, so perhaps they couldn't control the food.
If you have an Ipad or even Iphone, sounds terrible I know, it's just that sometimes these things are great distractors
I would ring and see if you can take something simple like sultana's or some sort of fruit even.
They should have enough toys to keep her distracted and hopefully with her age, they won't make you wait too long.
Hope all goes well