Rose CHOSE to give up her form and pass on her gem to Steven.
Meeting organic life, and especially humans, and especially Greg, pushed Pink towards realising how awful her civilization in general and she as an individual in particular are. But even though she started a rebellion to protect organic life, she still did questionable things (like hiding Bismuth) and inadvertently caused almost all Gems on Earth to get corrupted.
She realised that she could never be as good as the loveabale and compassionate humans that she wanted to protect. So she chose to pass on her powers to her half-human son in hopes that he would be more worthy of them. And he was.