Thank you!!! I'm a volunteer at a cat shelter, and I want to say thank you for opening up your heart and home to an older cat!!!
It can take up to a month for her to become completely comfortable. It really just depends on the cat. (Two of my cats took only 12 hours before they were sleeping on my head and ruling my house.) The best thing to do is to just stick to your normal schedule. Once she understands what your day is like, she'll become more calm. Don't throw any wild parties
for a while, and if you do have guests remind them not to chase after her becuase it might scare her. (Some people love cats that much. I almost got into trouble with Mer because a week after I brought him home the pizza boy tried to chase him down. Sigh.)
The vet trip should be okay. She'll probably hide for a day or so after you get her back home, but that's normal.
Take time for interactive play with her. You can buy all kinds of toys on strings, or mice you can throw, or even rolled up balls of paper.
I personally like using treats, but it's something that she'll expect for as long as you have her. Positive reinforcement works great with cats. It's how I got my kitten to be more comfortable around stangers, and grumpy Mr. Hans to stop growling at me and the other cats.
Again, thank you! Older cats really do make the best pets, and I think it was a wonderful choice for a first cat. Give her time and I'm sure you'll come to love her personality, because believe me, cats have huge ones. They just don't always show them to strangers.