Do you think Nintendo thought that far ahead? No bloody way would they say "Oh let's give her boobs for no reason, it's not to distinguish her as a girl at all."
Ruto was around that age as well and we could see those two bumps on her chest.
Let me also note that Beth had been smitten with Ralis which would mean if your theory is correct, then Beth is Bi-sexual. Now I think that would be going over board with Nintendos inside jokes.
I think Nintendo only changed genders when characters that look female are considered male. I don't think Ralis is a chick or else he'd probably look a bit more female (breasts.)