I can see both sides. On one side, she shouldn't have put them together, It wasn't her place to do so. On the other hand, I think you might be overreacting a tad. (Sorry if that sounds snide!) The first time they were put together, the dominant gelding felt the need to establish his dominance most likely. He wants to stay top dog. So, there's going to be some scuffs and cuts just from the pecking order establishing.
Then they were separated again. For weeks (Months?) When they were put together the second time, that last time they duked it out isn't valid anymore. They have to reestablish the pecking order all over again. I guess I can't really say without seeing the pictures of the wounds but unless they are together for a week or two, repeated separation and reintroduction is going to cause problems. It doesn't surprise me that he got a mark both times they were introduced. It doesn't seem like an aggressive gelding, just the standard 'aggressive; behavior that will come of him wanting to remain top dog.
BUT. Like I said. If you wanted them separated, and she put them together TWICE, that's not okay. If she's going to keep doing that, and you don't like it, you should certainly move. I don't really think it's fair to just isolate one of the horses away from the rest at all - it needs to be two and two or all together, and let them figure out the pecking order all by themselves. Marks will happen, but if you don't want the fighting you should definitely move the horse to where he'll be most comfortable and safe (And have buddies).