But, um, she's 16

I think she's probably more concerned with the 'not dying' part.
I'm not saying that Karl is the complete love of her life, but she's probably just got more sense than to try and revive him. And plus, she probably would have tried if Danielle hadn't dragged her off. And when Danni said 'I love you' it kind of brought Alex to her senses a little.
And I don't think Alex would try and bring Karl back just to spite Ben

I really don't understand you sometimes Roco

You seem so adamant that everyone loves Ben. I bet if Alex ran up to you and kicked you in the shin and yelled 'I hate Ben' while slapping Ben with a wet fish you'd still say 'But you love him really.'
