I imagine that would have been my reaction if it had happened to me (I'm really short, I would have seen nothing had I not been up front). Fortunately, my two friends and I arrived rather early (I'd guess 3PM) after a long road trip and chatted with someone in the ticket window who informed us of it. Given that we needed dinner anyways, it worked nicely.
And I'd agree that she definitely enjoys when people sing along to an extent - you can sometimes even see her form a smile when the rouse picks up a bit in the lively songs, but she definitely has a limit, and some songs just need their quiet atmosphere to accompany them. As far as requests and such, I'd imagine she's aware of them, because even Jack was joking about how she knows everybody wants her to play certain songs (..which was followed by jokes of using old copies of 11:11 as coffee coasters. He assured us he was joking, but I still can't help but cry on the inside).