Well, I'm not entirely sure, but my guess would be that bitter takes the definition of: resentful or cynical (dictionary.com)
So in other words, a bitter person (a cynical person) is very negative, and always thinks bad things about other people and themselves.
Some examples of a bitter person:
Me: "My teacher is very nice. He let us leave class 5 minutes early because we finished all our work."
Cynical friend: "He probably didn't want to be there."
Me: "Hey, why don't you talk to that girl?"
Cynical friend: "Because she wouldn't want to talk to me."
Me: "That was a close baseball game. It's too bad you lost."
Cynical friend: "Well, we SHOULD'VE won. If it weren't for the stupid umpire...."
Former beauty means: Used to be a beautiful person.
Hope that helps!
Student or Learner