Quote 1
"Can't you see she's busy with Angela's wedding dress? And why must you wear a silly costume like that? Really, Turtle, I don't know why you insist on making yourself ugly." (3.15)
These lines both compare/contrast Turtle and Angela, and swiftly highlight their mother's relationship with each of them. Notice how Grace privileges Angela over Turtle – her needs are always going to be more important. Even though the sisters are kind of doing the same thing – they're each dressing up as something they're not, or at least not ready to be – Grace hobbles Turtle and pushes Angela. Grace also makes it sound like the fact that Turtle's not as pretty as her sister is her fault, and under her control.
Quote 2
Her mother twisted the three strands into a braid. "I think you should wear your party dress tonight; you look so pretty in pink."
Pretty? She had never used that word before, not about her. What's going on? (9.21-22)
It's sad that when Grace finally calls Turtle pretty, Turtle automatically suspects that her mother has an ulterior motive. Grace hardly ever gives Turtle positive reinforcement, and Turtle simply doesn't trust her mother. This sadness is deepened by the fact that Turtle's right – Grace doesn't think Turtle looks pretty so much as she hopes to flatter her into giving up clues. There are two words for this: bad parenting.
Quote 3
Why bother with driving lessons, her mother said, anyone as pretty as you can always find a handsome young man to chauffeur you. She should have insisted. She should have said no just once to her mother, just once. It was too late now. (14.48)
Poor Angela. Between her beauty and her mother, she can't win. Here, we see how deeply both those things have damaged her. Her mother's used Angela's beauty as an excuse to keep her completely innocent, to the point of helplessness. She's tried to teach Angela to depend on her appearance, to the point where Angela can't even drive a car. Because of her beauty, she's actually become trapped and dependent.