Cariba Heine and Isabel Durant played Mermaids. Cariba Heine in H2O - Just Add Water (2006) as Rikki Chadwick and Isabel Durant in its spin-off Mako Mermaids (2013) as Ondina. Cariba Heine even appeared as Rikki on Mako Mermaids (2013) in its 4th season with Isabel Durant.
Cariba Heine is playing the character Isabelle. The actress who plays Grace is Isabel Durant. They have the same name minus the spelling of the name. They both plays mermaids on Mako Mermaids (2013) in the 2 final episodes of season 4 together (Durant main character) Cariba Heine even played the same role on H2O - Just Add Water (2006).