Hmm. That can actually make more problems, generally more often than not, when the boys interfere in henfights. Males and females have separate hierarchies involving only their own gender, after puberty they're not supposed to be fighting the other gender as they are not in competition with one another. I've kept many hundreds of chooks of many types over the years, hundreds of males as well, and only found mentally aberrant males, those with low instinct, try to fight hens or interfere in henfights, and it always causes problems, never solves them.
The third wheel is preventing the fight from coming to its natural conclusion, with a winner and a loser, making the two combatants bide their time, so every subsequent fight becomes more and more aggressive until you get incidents like this --- a serious injury seemingly out of the blue. I don't know if that's what happened with your hen, but it's very commonly the end result of having males who jump into henfights.
Pretty much as a rule, no matter the species, (I've seen it happen between cats, dogs, goats, horses, and more) --- if a third party regularly interferes in a hierarchy dispute between two other animals, it solves nothing, only delays the dispute being resolved thus increasing frustration, aggression and anxiety about the situation. This causes the two combatants to end up resolving their initial dispute with far greater violence than ever would have occurred if they'd just been left to sort it out the first time they tried to. It can lead to maimings, killings, and permanent 'bad blood' between individuals which would never have happened if the issue hadn't been protracted by continual interferences by an uninvolved extra.
You see the same thing happen when a human repeatedly removes a loser from fights, then reintroduces it a bit later; the alpha, the one who was winning, becomes more and more aggressive every time the loser is reintroduced, because from their point of view, the loser is showing disrespect; they don't understand the role of the third party, since it's not natural to them. The loser, likewise, having never had to show submissive behavior because the human keeps interfering / 'saving' it, continues from their interrupted 'save point' so to speak --- the loser battles the alpha again even though it can't win, since it doesn't know its place thoroughly yet --- and eventually (generally pretty quickly) the human removes the loser for the last time, generally with wounds, to recover for a while; next time they reintroduce it, it will be killed. Just because things were repeatedly prevented from coming to their natural conclusion.
This removing and reintroducing pattern is basically exactly how you bait animals of all species into fighting to the death; so is allowing them to scuffle then repeatedly interfering before it's resolved; these are actual processes people use to bait animals into killing fights rather than the usual swift and non-damaging hierarchy scuffles which they otherwise naturally engage in.
Chickens are showy animals, with many body language signals for threat, submission, etc, designed to prevent all conflict possible from a distance, and quickly put an end to all conflict possible. They are not naturally inclined to fight to the death over anything; a few kicks and pecks is generally all the average fight involves, whether it's between fully grown males or fully grown females. There is literally no greater seriousness between the fights of socially and instinctively balanced males and those of females, both genders resolve conflicts with a quick scuffle. That's all it takes to show them who is stronger, and the loser quickly signals submission, and the alpha just as quickly accepts it, and both go about their separate ways. That's among instinctively normal chooks of course, not those which are mentally aberrant. They are geared to avoiding all violence possible... Except for some mentally aberrant and vicious individuals which prefer to kill, of course.
There is an additional danger in this scenario of males attacking fighting hens, because chickens are frontal fighters, who do not show their flanks or rears to animals they are battling; their fused skeletons and meaty breasts afford their internal organs a lot of protection that is completely absent from their flanks and rears, and attacks from those angles (such as occurs when a rooster attacks two sparring hens) can break eggs inside them or damage internal organs, break bones, etc, far easier than attacks from the front can. Very dangerous.
I never had problems with violence between my hens for years, until someone gave me a silly little male who would always barrel into every mild scuffle between hens and make it a full blown three-party fight. Violence and injuries increased dramatically from that point onwards until I got rid of him, then it went back to the usual non serious, occasional scuffling levels, the normal hierarchy shuffling that occurs pretty much on a regular basis.
Many people will tell you it's normal and natural for males to break up henfights but it's not natural to the species, as many other domestic traits also aren't. Males coercing matings despite rejections from the hens, and abusing hens, both genders killing chicks, committing cannibalism, mutilating one another, feather picking and so forth also aren't traits normal to the species. Some people forget that instincts are altered in domestic animals, i.e. brooding instinct being bred out of some lines and so many neurotic traits being bred in, and they think anything they see among their domestics is 'just how they are'. No, it's not so simple at all.
Those same people telling you it's natural for males to break up henfights pretty much as a rule have extreme violence in their flocks, precisely because of the aggravated hierarchy-settling issues caused by these 'third wheels'. The hens don't naturally interfere in male fights, and males don't naturally interfere in henfights.
Anyway, best wishes with sorting out your issues there. Your flock is only young, by the sounds of it, and time can 'iron out' many confused or warped instincts into a form more natural to the species.
