Is Yukiko a little too OP?

I'm playing P4G and I very rarely use my main (currently at Lvl. 45, and just waiting for the final party member for the next castle, which may pretty obviously be Naoto. Idk for sure because I'm coming in blind) and at this point everyone else pretty much covers for it, but I just happen to always choose Yukiko despite her downside of not having any Physical skills because her SP is almost always full. Why is that? Does she just never run out of it or does she have a passive that I am not seeing?