Noahsmommy,
That really sucks that your friend let you down. What really bothered me was the dirty syringe. We're talking about your cats health here. Totally unacceptable.
As far as calling her on it, you're probably right about upsetting her. And like Johanna said, if she was that great a friend, she would've done what was expected of her. If she should ask why you got another sitter, THEN I'd be honest with her.
Vet techs and assistants are GREAT pet sitters. Not only can they care for your pets, but if an emergency arises, they'll know what to do.
God forbid if something happened to one of your cats while you were gone. That dirty syringe really has me hopping mad :mad: