Louise

H2O: Just Add Water - 1x23 - In Too Deep

Louise Chatham, was one of the three original mermaids. She was best friends with Julia (last name unknown) and Gracie (last name unknown).
She is the past version of Emma Gilbert, and it is rumored that she may have the same powers as Emma.

Ms. Chatham

H2O: Just Add Water - 1x23 - In Too Deep