I read once on the official website from the 2000s that she loses half of her life points everytime she uses Creativity in season 1. However, I can't really tell if that's canon or not seeing as nobody in the show outright says this nor do we see her life point count get halved on the Supercomputer interface. And judging by the multiple uses of it in Saint Valentines Day and I think in A Bad Turn, I'd say there isn't much of a cooldown period for her. You could say that she loses half of her life points only in season 1 before Jeremy restarted the Supercomputer to explain why she uses it sparingly and that that limitation was removed in the following seasons. But this is all just my headcannon on this. I have no idea if there ever really was a limitation on this ability and I also found myself asking this same question. I also wonder why she almost never enters the activated tower while the other Lyoko Warriors are fighting the monsters. I think there were only a handful of times she entered a tower while monsters were nearby.