I think Ascoeur is simply missing experience. While the lesson itself largely went up in smoke when Dia powered her up, Ascoeur learned about her limitations rather quickly. Once she gained power, she was a lot better at using them more discretely, and she fought a lot more conservatively.

We can't forget that these are not trained veterans like Troyes Jeanne, Trixie, Tweedledee, or any of the ES members from last season. They aren't even officially employed as agents.

When things get a lot more serious, I think Ascoeur scales back her peppiness and idiotic behavior until the crisis is over. She was very quick to tell Q-feuille to run and leave her alone with both of those two. Her original plan seemed to be to have Q-fueille get Dia to safety and then teleport away herself. The only problem was that Q-fueille didn't listen to Ascoeur and got caught by Saphir, and Rubis figured out Ascoeur's weaknesses.

She could probably beat any other ES members at infiltration missions if she shut up long enough to do it, but I'm convinced that all depends on the severity of the mission, and the experience to know how many on relying on you. For something like pumpkin pudding, she doesn't have to be serious and can afford to screw up the whole time. Rescuing a captured VIP hostage, or stopping terrorists isolated in a bunker? I think for all her faults she would take those kinds of missions as seriously as Q-feuille does, at least until they are over.