I take it there is some kind of pun or word play using the わ/ワ characters going on?
No idea, but I did go back and update the 3rd page with a TN, since wakame is a type of edible brown seaweed, and Koume's wavy hair could be said to be similar in color and form. It's like remembering someone's name as "megane" (glasses) just because they wear glasses. It's probably intended to be humorous, and add a bit more to the punch-line of Miho forgetting Koume's name.
As for the other "wa" of wani (gator), it has to do with the infamous manga page of Phase Erika (post #2485194) where the artist mistakenly used "wani" instead of "wayo", and Erika being associated with alligators ever since.
