Well, first off I don't think we've entirely figured out that we're dreaming. There's not really been a lucidity trigger, yet.
Secondly, apparently Yuuka doesn't exist. Or if she does, she's completely unknown, which would be odd.
Thirdly, Reimu tends to go for the obvious things first, especially when in beatings mode, which I'd argue she's well into by now, as someone has tried to erase her and her work from existence.
Yuuka might be a second option, though, if beating up Moriyas doesn't work.