Okay I'm going to make a short remembrance of the film she's from. Disney put almost no effort into making an original plot with this one, they just wanted some quick cash, and that's all one needs to know before watching Return to the Sea.
Despite that though, I think I'm through being angry at Melody herself, I can't find much to hate. She actually had tried the sea before and loved (unlike her mother, who could not have had that much experience on land). She also didn't want to impress any boys she had known for 15 minutes (tops) and it helps that Morgana was more subtle about her evil intentions than Ursula. I guess what I'm trying to say is that if this had been the only Little Mermaid movie, I might have liked it, but these were just good ideas too late.
I should also mention that I have recently discovered "The Little Mermaid II: Pinball Frenzy" for the Game Boy Color. It's hard to stay mad at Melody with a game like that. Finally, unlike her mother, Melody isn't part of a cash cow franchise for Disney that can easily tell girls to stay in the kitchen (in case you were wondering, that is the Disney Princesses).