I can clearly see OP's daughter (and me) answering "okay?" in that puzzled, raised eyebrow, trailing and audible question mark that could translate as "why are you telling me this?".
Lovestruck and/or socially not there teenager could interpret this as an agreement, but for me the daughter is in the clear.
There could have been better communication all around, but it's on Jay to have jumped to hope/conclusion and bought the tickets, he probably spun a tale to his mom, maybe to explain why he already had bought, rented and made reservations, or he really believes it, or thought his mommy would make the DD go to the dance with him....
They're teenagers, knowing adults sometime have trouble navigating communication, I'm not surprised of the hiccups.