"You should tell her that all the COOL KIDS on The Pill love the Happy Birthday song!"
Score one for you.
Since it was accidental (friend forgot, and left an apologetic message) it's a tougher call. It could be that BCQ thought she was doing it on purpose (hanging up is rude, but hanging up on someone being rude is more acceptable in my mind), but when friend apologized BCQ should have accepted and apologized as well. If she did and you didn't mention it, then I'd say all is well. If not, then she gets e-purgatory at least.