Minnie's bathroom problem is much improved after almost a week on antibiotics. There were two normal-sized pee clumps in the box this morning.
Everycat tells me that bad stress can prompt an inflamation of the bladder in girl kitties, and Minnie's problem did arise immediately after I had the repairmen in to work on the furnace. Her favorite hiding place is under the furnace, so I guess she thought she had nowhere safe to go. Silly cat, there are two beds in the house, plus a couch with a nice hiding space behind it! Maybe she needs something she can crawl into and (figuratively, anyway) shut the door behind her, something well padded to block out some sound, with a flap or something she can burrow under. I've probably just invented something that doesn't exist, but I'll research cat furniture for something that looks like a portable hidey-hole.
The couch Minnie peed/leaked on has also improved, although I'll reserve final judgment on the remedy until I've had a chance to flop on it for a while this evening. Alas, the Nature's Miracle did not cut the mustard (or the stench), so I tried something else by Woolite. I'll let you know if it really worked.