Hi JillyBeans,
Sorry, no dogs allowed at the pools. No exceptions. You cannot get a guest ID for a dog.
Understanding your worry, though, about leaving your little girl by herself in a strange place, let me recommend something that I've recently found that will probably help her stay calm. It is called "Thundershirt" and it is made out of a stretchy material. It is adjustable and comes in teeny sizes, too. I have a little 5 lb poodle that is very skittish (she was rescued as a breeding dog) and this shirt works wonders for her.
The Thundershirt feels like a hug, which is very calming and soothing. It doesn't work on all dogs (DuffysMom says it doesn't work on her little dog), but it might be worth a try for you since your little girl is probably nervous when you leave her no matter where you are or what the situation.
Here is their website. Take a look:
http://www.thundershirt.com/
Watch the videos on their site. I ordered the little pink one for my poodle and I use it when we go for golfcart rides, when the vacuum cleaner is on, and when there are workers in our yard. She usually goes crazy for these things, but with the shirt on, she settles down and calmly watches or just takes a nap.