Aside from Kara herself being powerful, this parallel universe had effectively already been conquered.
All the remaining Red Star Reactors were successfully detonated, after which the Multiverse Justice League took this universe under its wing.
Because of the earlier massacre of civilizations across the universe, the entire parallel universe had an extremely low level of technology. The Kryptonian lunatics exposed to red star radiation lost their superpowers and were too weak even to push open the life-support pods holding them.
Working together, Firestorm and Flash converted most of the Kryptonian bases into prisons floating in space.
The cleanup that followed would be particularly lengthy. They needed to inform every civilization in this universe that had suffered a massacre, then find factions with enough credibility to pass judgment on these Kryptonian executioners.
Moreover, because of Kara's earlier actions, some of the Kryptonian bases were already empty, their lunatic occupants having escaped. To prevent anything similar from happening again, they would have to assign personnel to hunt down these lunatics who still possessed superpowers.
Kara, meanwhile, had lost her superpowers and was taken by Superman to the Multiverse Justice League's Ark Prison on Earth One.
This prison was also Brad's handiwork, built specifically to hold criminals who might endanger the entire multiversal system.
The conquest of Nekron's universe was postponed. That place was even more dangerous than the universe of Kryptonian lunatics. After the incident with Kara, even Superman had come to understand that powerful superpowers alone were nowhere near enough.
A civilization capable of continual advancement was what truly deserved to be feared.
If the universe of Kryptonian lunatics had continued operating for another century or so, and Kara had truly raised those pure new Kryptonians on New Krypton, the resources of the entire universe would have fueled Kryptonian civilization's development.