She was giving him CPR and she gave him that smile because he opened his eyes and was awake.

yes surprise me rikki giving her kiss on will as cpr wow !!!

she was saving his life, not kissing him lol he would have died if she didn't give him that oxygen.

yes. But the romantic music and girly smile. It sure looked more than it did.

it techincally was an "oxygen supply", but the scene was shoot in the way it could look as more than that.

what I find lovely in "H2o just add water" is that the director/screenwriter don't take the part of this or that character and try to let the audience come to their conclusions, according to what they feel and think.

this doesn't mean the series is ambiguous. it has some "moral perspective" over events, but it isn't cutting everything down to just good and just bad.
this is positive and "advanced" for a kids/teens series (though I'm not a teen anymore and I still watch it :) ).