Wow, that’s quite an unusual situation. Captive bred seahorses are raised at far greater population densities than wild seahorses ever experience, and they are normally quite gregarious as a result. They are accustomed to being around other seahorses and ordinarily appreciate one another’s company very much. As a rule, the males do everything in their power to attract the attention of the females, so it is very unusual for amorous males to run off a female.
Right now, it seems that both the males are smitten with the same female and want nothing to do with the other filly at the moment. In the aquarium, seahorses do often work out a dominance hierarchy of sorts within the herd, and right now it seems that your isolated female is at the bottom of the totem pole as a result.
But that could change for the better, and is likely to before long. Sooner or later, the popular female will pair up with one of her suitors, and when she does, the other stallion is going to be the odd-man out. Once that happens, you can bet your isolated female is going to start looking a lot more attractive to the male that was spurned. And that will put her on a more equal footing with the other seahorses.
In the meantime, there’s not a great deal you can do about the situation. If the others will not allow her to join them at the feeding station right now, you’ll need to target feed the isolated female to make sure that she’s getting enough to eat.
Another thing you might consider is to set up a second feeding station. Train the seahorses to eat from both feeders, and then if your isolated female doesn’t feel welcome at the communal feeding trough the others are using at the moment, she can have the other one all to herself.
Best of luck resolving the situation with your social outcast, Seagazer!