I'd say the only ones that would be already taken are Shiva for a later appearance, and somewhat more obviously... Knights of the Round.

Hoshi being combat focused, could be something like Ravana or Susano (Doesn't need to be actual SUMMONS but just like... things that have been summoned in FF history). Those would depend on how much she actually enjoys fighting and competition. They both love combat and being challenged, just one is fire aspected, the other is water.