chinchillas doomed to not getting along?

We recently got another chinchilla, ChiChi, who's over a year old. When we first got her, we put her in a cage with our other chinchilla, Frida, who's about 9 months old. (which, yes, was a big mistake on my part. I researched enough about chinchillas when they're independent, but not how to introduce them.) Frida was mounting ChiChi at first, and I can't remember what exactly ChiChi did afterwards, but it really scared Frida and she was standing still in the corner of her cage. We kept them separated after that. The next day, we let them both out to play, but they started fighting and fur was lost. We kept their cages next to each other for the next week. Then when we got a new cage, we put them together because it was neutral territory. that didn't work out either. Again, fur was lost. Now we've switched their cages in hopes that they get used to each other's scent. I really hope they aren't incompatible, but I feel like this could be because they got off to a rough start. What do you guys think? Should we not try to put them together again? Or should we possibly wait longer to see if they could possibly still get along?

There are several reasons for a 30 day quarantine of a new chin. First the 30 days helps prevent the spread of illness if the new chin is sick it give it time to show itself, but also it allows the new chin to settle in to it's new home. It also allows you to get to know the new chin, how much does she eat, drink, what are her poops like, what is her personality like, etc. That way you will know quicker when something is wrong because you'll know what normal is for her.

Chinchillas especially females are territorial, so yes as you said big mistake throwing them together in one cage, especially one that is already owned. So long as no blood was drawn (which signifies intent to kill, in which case you can't trust them together ever) I would just separate them, ideally in separate rooms if possible for a month. Let them both reset and forget about what happened. Then bring them back into the same room, or if you couldn't put them in different rooms then just start moving the cages closer together. Intros most of the time take weeks, months, and sometimes years, you can't rush it or it will fail and you will have to slow down even more for it to work. Think of it like having some stranger move into your house with you, chances are you need time to get to know them to trust them and become friends. It's not something that happens quickly, and not all chins want a friend, and not all chins who even want a friend get along with all other chins.

So basically, my suggestion, since you went too quickly the first time, is separate them for a few weeks, then slowly over the course of a few more weeks bring the cages closer together. Try short play times together (after a few weeks apart) if they seem to be getting along in cages near each other (no spraying or trying to bite). Then when/if they are getting along during playtime then try swapping cages, used a neutral cage (if you have a third cage), or scrub down one of the existing cages, replacing everything so it's neutral. The slower you go the better chance of success, you have to go at the chin's pace not yours, there is not such thing as too slow for intros.