Panel 1 Wider, Isabelle turns herself around, still on all fours so her ass is facing the dam, the water spraying her growing size down.
Isa “Not fair that Annabelle has been getting all the growthy attention lately, let’s show her how it’s really done!”
Panel 2 Isabelle smashes her rump and against the wall, forcing the spraying water to flowing inside her. Her ass responding by swelling faster than the rest of her, her thickness expanding even more, to almost beyond cartoonish proportions. Pose reference:
Panel 3 and 4 smaller panels; same panel with her growing bigger between the two. From behind the dam(side with the water), we see her ass expanding up and over the wall
Panel 5
Happy that her size has grown even more, she rears up on her feet, her ass now pushing back dangerously on the dam.
Isabelle “I guess we could just use the lake as a bathtub…..