Not sure if I should bring in one more cat

I'm considering bringing one more cat into my house (I already have four in here). The "new" cat is actually a 13-15 y/o female who has lived outside her entire life. My inside cats are somewhat familiar with her as they have seen her through the sliding glass door everyday for several years.

Is there anyway I can tell before bringing her in if she will get along with my other cats? I know I'm supposed to do an introduction period, but I need to have some idea as to how they will all get along before I do anything. I don't want to bring her in and do the introduction thing only to find out the other cats are miserable because of her presence. If that happened then I would have to send her back outside and I think that would be cruel. She is the bossiest cat I have ever seen and I could certainly see where there would be a "fight" for dominance.

My other cats have been allowed to sniff her for a minute or two recently. Thankfully, none of them hissed. One of the females had an expression of worry, but that's the only bad thing I noticed.

Does anyone have any advice? The last thing I want to do is make any of the cats miserable.

Thanks for the replies.

I usually do a three month long introduction period. Part of that is to keep the new cat in quarantine to observe for any possible illnesses since I don't do the distemper vaccination. The vets around here only do FeLV and FIV testing.

Currently, I have a total of four cats in the house. Three of them are 6 y/o siblings (two females and one male) and the fourth cat is a 11 y/o female. The male is totally laid back and friendly. The one 6 y/o female is timid but I think she might be bossy, it's hard to tell. Her sister is a little timid but I think she might be a little bossy too. She definitely is one to get jealous of other cats taking my attention away from her. She is nothing but a kitten trapped in an adult body and that seems to make her annoying to the other cats sometimes. The 11 y/o used to live outside for 8 years and was very timid and got bullied by other cats. Since bringing her inside her personality has changed. She's still a little timid but I think she is the alpha cat. I've seen her "slapping" the other three cats for no apparent reason at all. Since her brother Fuzzy died several months ago I've noticed that she's having more friendly interactions with the other three cats, but she's also slapping them more. However, she is very anti-social with the other cats, except that she wasn't like that with her brother.

Since Fuzzy died four months ago, I've noticed that the cats seem to get along better. There's less stress among everyone (humans included) and the cats seem to be more playful. I don't understand that. Fuzzy seemed to be laid back and friendly. He certainly wasn't agressive and didn't bully the other cats. He always tried to mind his own business. If anything, the two younger females may have tried to antagonize him. Other than that the only thing I can figure is that perhaps he was in pain and/or stressed out from his health problems. He did have a kidney stone for nearly the entire length of time the three younger cats were in the house.

I think the outside cat, Nani, will be ok inside. She's actually been locked in my garage for the past week because of a dog that keeps getting loose and is known to kill cats. That's really the only reason why I'm considering bringing her inside right now. I was planning on bringing her inside later this year or early next year. But there's no way to know when the dog is going to get loose and I get scared for her safety. I heard the owner of the dog is trying to fix the problem but that doesn't really help with this decision since I don't trust the guy.

I thought that was a good sign too, but wasn't sure. The inside cats seem to know that she belongs here. What I mean by that is that when a stray cat comes around and they see it through the sliding glass door, they seem to know that it doesn't belong based on their reactions to it.

That is a great idea. I never thought of doing that. Thanks.