Update

Sushi demonstrates how one uses a towel to keep a rat upright.

Sushi is slowly bouncing back, although very slowly. Being sick for so long is obviously taking its toll, yet the little girl is a trooper. She's taking her medicine without a struggle, tolerating the horrible fluid injections with hardly a fight, and still manages to look happy to see us. She is eating her regular food now (in addition to liquid food we hand feed three times a day) and is walking around more, although she's definitely not as light on her feet as is normal. She is still a bit unstable when cleaning herself, but at  least she is feeling well enough to groom. She isn't out of the woods but she is doing well enough that I'm not terrified I'll find her dead every time I look in the cage.

The girls are separated again, because Sushi is too weak to navigate the ramp or stop her sister from pushing her around. Saké isn't pleased with the state of things.

Saké nests in the litter tray.

Hopefully Sushi continues to improve and they can be back together soon.