If you've been paying proper attention to the list so far, this should already be obvious to you, but her treatment was so atrocious that we think it deserves to be a point in its own right. Let's go over the facts again.
Judy Garland was working from 4am to 8pm, six days a week, at age 16. She was being given drugs to control her weight and keep her awake. She was being molested by other members of the cast. She was being physically abused by the director. She was made to wear a corset to disguise the fact she had breasts. Producer Louis B. Meyer spied on her to make sure she wasn't eating things he didn't approve of. Garland's self-image was so negatively impacted that she once said 'I was frightful - a fat little pig in pigtails'. If going through that is what's required to become a movie star, we don't want it.