I did actually have Angel in the sketch, but it just felt a little weird having him there, even though ponies don't normally wear clothes anyway. :E So Fluttershy got to have some private time to relax -- she deserves a quiet moment to herself now and then anyway.
I used this brush by ~KoiFishSushi. (It's also what I used for most of the sketchy/crayony stuff I've been putting up lately, it's a really nice brush to doodle with.)
She fretted that one of her real ducks might get jealous if she used an artificial substitute. Of course, the ducks NEVER join her for a BUBBLE bath, since it would strip the oils from their feathers, which would interfere with flight, water-proofness, and perhaps even insulation.