Hi C.A.,
Okee Dokee.... Some IDEAS!!!!
(I totally agree with you, the ONLY WAY to have and keep cats safe & healthy is indoors!)
~ Since they are ALL indoor animals, they (dogs & cats) ALL have a common environment (your home!).
*A general method is as follows:
(1) "IF" at all possible, keep the "new" one in a separate room. (Guest room if you have one.)
[Boy, I feel sorry for the person that had to use their ONE and ONLY bathroom as the designated / segregated room!!!]
~ As I suggested earlier, while she's in "quarantine" is the perfect time for spaying...gives her a peaceful place to recoup.
The "Introduction begins...."
(2) The "new" critter comes into the common area in a crate.
(3) The beginning "visits" should be often and for short periods of time with close observation.
(4) Set the crate in an out of the way area (not the path to the backyard or "litter box"). LOL :D
* Some people have had successful experiences with one of the "calming sprays" [brand name: At Ease made by NaturVet, natural herbal calming spray for cats] available from pet stores. (I have this particular one.)
* Before putting the new cat in the crate, spray a little onto the towel (or blanket) in the crate. Spray on BOTH (ALL) animals ... where they have a hard time licking it off (back of the neck is a good place).
* I would expect your herd of Chi will have no problem after a short period of time. (Even though she's not used to dogs, the other cat will be the bigger problem/concern).
(5) Provide multiple litter boxes (hopefully away from possible kitty fudge eaters - if you have any! ha!)
* You will be able to judge the reactions and interactions, after all your years of animal behavior observations.
* If the "newbe" is C@@L with the dogs after a short period of time... (that's what usually happens, the cat to cat will usually take the longest) then invite some of the mellow dogs into the "guest room" for a face to face have the cat in the crate before the dogs come in. Then open the crate and see what happens. This is usually very "entertaining". The Chi "NOSINESS", "curiousness" and "big dog" mentality will encourage the new girl to "make friends".
* If that goes well.... bring in the herd!!! Repeat the procedure.
(6) REMEMBER, while all this "doggie dance" is going on the visitation in the crate common area should continue.
* Someone else mentioned the scent being on "everybody" and carried back and forth.... if you add the "*Calm Spray" to the "mix" you're ready for the cat to cat intro.
(7) If you exercise all the dogs at the same time in your yard...that's a quiet time to take the OLD ONE (6 months older!) into visit the "guest". (Don't forget the spray on/in crate and cats.)
~ Try it with the crate closed..... if you're impression is positive ... unlock the gate .... open the door a few inches... and see what happens. (*In the old days some of us used "perfume" to blend the smells/scents ... now they've got that "magic" herbal spray, which seems to work on MOST cats.)
~ Because you BOTH are animal lovers and are calm that will have an affect, too!!! The division of attention will make everything easier... to sets of eyes and 4 hands will help, too!!! :D
If you do the common area visits many times a day, the dogs visits and intro goes as fast as you/we'd expect ... then the cat meeting should be possible within a matter of a few days.
* Someone else suggested several websites that give suggestions too. I plan on going there and reading to see if "they" know something really "good"!!!
You and your hubby are up for the "GOLD STAR" ON YOUR FOREHEAD AWARD!!!! Relax, expect the best and you should have a great addition to the family.
Good Luck! Can't wait to learn about your success and the short time it took to accomplish the "deed".