Gap is indeed the correct term; that's where "Gap Moe" as a concept is derived from. We've seen her outward behaviour change a little according to her inner feelings before, so it's not just that she's outwardly cool all the time, either. Any time she gets jealous and acts upon it, she shows her Gap.There's got to be a term for being outwardly one type, but it's a mistaken representation of your true inner type. Gap, maybe, but Gaps tend to be a mix of both types. I'm talking about when the outward type is purely imagined by other people.
Here the Cool Gal is actually panicking inside. Maximum shy becomes cool.