Her fight against Set. The Avengers get word that he's in town, so they call in just about every hero in MC2 to their headquarters to discuss it...but leave out Mayday because they're afraid she'll get hurt. Unfortunately for them, gathering at their headquarters is exactly what Set wants, and he uses his power to trap them there. Unfortunately for Set, May finds out about this, and goes to take him on. She manages to hold her own despite the overwhelming disadvantages, and her fight lasts long enough, and distracts Set enough, to let the Avengers escape. She passes out from exhaustion just as they arrive, and wakes up to find she's earned the respect of every one of those heroes.