Ranma 1/2 Memorial Book gives Shampoo's name as:

Sha n pu <vowel extension mark>

Henceforth, I shall give her name as "Shampoo" when normally addressed
(English translation stuff) and Shan Puu as her formal Chinese name.

------

Uh..."shanpuu" would be the Japanese name which directly corresponds to
"Shampoo".   That "Shan Puu" isn't meant to be her Chinese name, methinks.
I still think that her chinese name is meant to be an exercise to the
reader.