sounds like my cat. He died when he was about 18 years. He was a bit senile towards the end.
My vet told me to ignore him when he wakened me during the night, but this is almost impossible. Even shouting them is seen as attention - you can't win. I used to sleep with a waterpistol under my pillow, but by the time I got ready to aim he was away doing something else equally annoying.
Being extra vocal can be a sign of thyroid problems, but if your vet said she is okay he will have checked for that.
Everybody that I know with old cats seem to have the same problem. I tried locking him out of the bedroom, but the screaming and scratching was pathetic and pretty loud.
I now have two 18 month old cats - my problem is them running around the house during the night. They sound as if they are trashing the place. It seems that chasing each other up and down the stairs for what seems like hours on end is fun for cats!
Good luck with your cat, annoying as she has become I am sure that you still love her loads.