Hear ye, hear ye!! The Shower Is Fixed!
Jeremiah, most excellent of husbands, has fiddled with it with his Man Tools and fixed it.
I really don't know what he did, or what was wrong with it, but it's fixed now and with New, Improved water pressure! I suppose there must have been some sort of blockage that slowly reduced the pressure until the whole pipes freezing thing was the last straw. But now it's back, baby :) It helps to be able to take a nice hot shower after a full day of being pooped on by a one and a half year old. Which, by the way, D., is waaaaay worse than being pooped on by a newborn, so enjoy it while you can ;)