There was one more time Miyu was seen in the 
bath -- and it more closely matches this cel. In 
the flashback episode (22), showing Miyu as a 
child, Miyu's mother draws a bath for Miyu's 
father (who is dead). Miyu uses it instead. I 
think the cel is from this scene. Notice Miyu's 
hair is down, and when Shinma En-jyu is washing 
Miyu's back in episode 4, her hair is not only 
up, but she's not sitting in a real bath. (She 
only takes off the top of her kimono.)

Standard disclaimer of me saying this without 
checking my DVDs first. ^_~

Many Sharp Smiles,
--Drac