Wayne,

I NEVER expose any new kitty to my family until they've been to the vet and gotten a clean bill of health. But that's how I do things. I know everyone is different. I would hate to have your kitties' health compromised.

Never say NEVER. You say:

I had a strong suspicion that she was OK healthwise, because of her being spayed and living outside without becoming sick. She was obviously some one's pet that probably had been dumped. so, I am sure she has had her vaccinations, along with her spaying.
Could she have been dumped because she was pregnant with kittens? Alot of times the vets can't even tell a cat is spayed until they shave the area and locate a scar. I would also have her tested for feline aids and leukemia. If she is a carrier, then you have just exposed all your other cats to her. I would think twice about having her looked at by a vet. Just my humble opinion.