Hello! That's totally ok. So, outside of battle, they can use it as much as they want. Inside a battle, keep in mind that everytime a player does an action, the world does a reaction. So if they heal as their action, the monster or threat will then react. So they could get hit, or part of the situation gets worse to pull their attention. But there isn't a limit on how often one can use their powers, it's all about what choices they need to make.
You can summon it each time it's defeated. You only ever get one. You can't summon multiples.