Timpani sent in several questions, so I'll break this down and answer them by section.
I had a question because we recently took an abandoned
cat into our home. Our neighbors moved out and left
about 6 cats, including the cat we took in. She has
been in our home for a few weeks.
We gave her a flea shampooing, and her own litter box,
since we have two other cats (ages 10 & 11). Should we
have done anything else before bringing her inside?
Since you have two other cats, I would have her tested for feline leukemia virus (FeLV) and feline AIDS (Feline Immunodeficiency Virus...FIV). This is a quick and simple blood test that any vet can do in their clinic in about 10 minutes. Both of these are contagious diseases for which there is no cure or effective treatment. Casual contact shouldn't trasmit FeLV or FIV, but if any fights happen, it could happen. Also have the cat tested for intestinal parasites. Roundworms, hookworms, and coccidia are the most likely risks, and all could be potentially contagious if your other cats come into contact with her feces (such as getting into her litterbox). All are treatable, but you want to minimize any risks.
And, she keeps getting outside (I think she was mainly
an outside cat) and going back to the empty house
where her siblings are still hanging around. How do we
keep her inside, or make her want to stay inside?
That's a great question! And unfortunately, not one with an easy answer. Once a cat gets used to being outside, it's very difficult to make them want to stay inside. Very little can make the inside of a home more appealing than outside. Usually all you can do is be very careful about letting her outside, especially if she's near a door when it opens.
Also, she goes pee in the litter box, but she goes
poop in the bath tub. Which is probably the most
convenient place for a cat to poop, but, how do I get
her to go in her litter box? She likes to scratch,
I've seen her poop in my garden, and then bury it, so
I know she likes to bury it.
If a cat is used to using the bathroom outside, it can be difficult to get them to use a litterbox. First, I'd recommend getting Feliway (read yesterday's post) to reduce stress. Then, find a brand of cat litter called Cat Attract. I've had good luck with clients having problems with their cats going outside of the litterbox. Pet specialty stores such as Pet Co and PETsMART should carry it. To help train her, start with her in a small room, and don't let her out until she is consistently using the litterbox. Then put her in a larger room, and so on, making sure she's using the litterbox each time before allowing her in a larger space.
She's looks between 5-9 months old, but I can't be
sure. What shots will she be getting when we take her
to the vet? And should we just get her fixed at the
same time or wait?
Definitely take her to a vet. The vet should be able to tell her age pretty accurately (it's something we do every day). I would recommend getting the feline distemper (FVRCP), FeLV, and rabies vaccines. Those are very important vaccines, and rabies is required by law. Check with the vet, but most veterinarians won't schedule a spay for a pet that they've never seen before. However, you should definitely plan on getting her spayed soon. A cat in heat is NOT fun to have around, and being unspayed increases her risk of certain kinds of cancer.
Keep those questions coming!