1. The skull did indeed come from her costume, though he doesn't need to speak to her to confirm this. The float requires a variety of people working on it, so he can ask any one of the designers or organizers.

2. He won't be able to find her. Significantly, it won't be due to her hiding or warding herself. She's just vanished as if she never existed. Kyle may spot others "hiding" in back rooms and other corners throughout his search, but they'll just be the usual types who are drunk, asleep, or having intimate relations.