The aging thing seems like it might be true for merpeople. But how about true heartbreak can kill them, like they turn into bubbles or something. (That's how the original Little Mermaid ended, she turned into bubbles!) But also maybe some merpeople can choose the age they want to stop aging. Like merpeople who desire the rank of elder has to look the part! Think Ariel's dad, how he obviously had some age on him. 

So they age slowly, but can still die sooner than their time if something happens to them (heartbreak, illness, murdering fiend lol )

But maybe the aging thing also will affect a human if they are bonded to one? 

Also I like her gaining her feet again, because it does open the RP for a lot more.

((I really liked the H20 show. They came out with a sequel that I haven't seen yet. Hope it is good, but the cast is all different. ))