Huh. Tough one. I was immediately going to say no but after noticing that hand placement, it's hard to say. I am leaning more towards no than yes though. Doesn't mean she isn't ticklish or her underarms aren't ticklish, just that in this particular situation, I feel that it is more likely than not that tickling is not occurring. She is smiling, but she's also in both an accomplishing and incredibly risky pose and it's requiring quite a lot of strain both on her part to keep her body straight, and all the other girls to hold her up.
I feel like even if there was tickling, it's the last thing on anyone's minds. Sometimes when tickling occurs in a stressful or busy/complicated situation, it doesn't always register. She could be getting tickled, but she so focused and the girl holding her is so focused, neither is really thinking about it. Cheerleaders is tough.