Miss Melly is mewing (it sort of sounds like chirping), I think mostly for attention since it doesn't sound as pained as her mewling this morning. I was going to go in and cuddle her a bit, but Scarlett wandered over just as I was opening the door. She caught a glimpse of Melly through the door crack, and promptly started hissing. If Melly hissed back, I couldn't hear.
Here's the part that might be progress: Scarlett, while definitely in an offensive sort of stance - low to the ground, head down, tail down - did not puff up! No tail puffing at all! Nor was there angry tail waving! She did growl quite a bit, which was unnerving. I stood and held the door cracked about 1/4", and Scarlett growled for a few minutes. I couldn't see what Melly was doing, but she didn't seem to be moving around much. After a while, Scarlett backed away veeeery slowly. As soon as I closed the door and took a couple of steps away, up went Scarlett's tail into the familiar crook position, and she started sniffing my slippers and rubbing against my legs.
I'm currently baking some plain chicken, bits of which will be fed to the girls on either side of the bathroom door. I'm not sure this strategy will work on Scarlett given that she won't even look at a treat within five feet of the door, but chicken's her favorite, so we'll see.
And here we have Scarlett casually keeping an ear out for Melly. You can also see Scarlett's catnip mouse, disciplinary squirt bottle, and the peed-upon bathmat.
This is from this morning. It looks like Melly is about to attack my toes, but she is actually stalking the faucet drips. She did that for about ten minutes, and would periodically lunge at the drops as they fell. Of course she'd land in a heap and the drop would fall on her head.