OK, I'll just come out and say what I really suspect: She became incredibly famous as a child actress and wanted to return to as close an approximation of childhood as she could. She was photographed thousands of times and celebrated widely as a precocious, adorable little girl, and a busty sexpot body just wasn't how she saw herself. Her desire was to remain a child, which is impossible, but no one was willing to tell her that.
And Frye's mother, who doubtless enjoyed many perks from her children's childhood acting careers, may have been eager to see her return to less extravagantly feminine proportions.
This is hardly unique - Michael Jackson has pursued the exact same "Peter Pan" goal, and remaining childlike is an obvious tactic for child stars to extend their earning years. Two of the most enduring child stars were Davy Jones and Mickey Rooney, neither of whom ever attained adult stature. And not to go all X-Files on you, but there are some people who think that Jackson's father imposed
very drastic surgical measures to keep his meal ticket functional.