I dont think that Soo Ah needs to be forgiven or anything. I think its is fine, as long as she can reflect on her past actions and through that become a better person (or in her case: become a person and not an image in the first place), she should get a chance to redeem herself. People shouldnt get judged by their past mistakes if they make an honest effort to overcome them. Yes, people make mistakes and some of them are worse then others, but in general I dont think any person is beyond redemption, unless they are unwilling or unable to strive for it. Its true that her past doesnt excuse her behavior but it explains it. She didnt trample on other peoples "feelings" because she really liked it, she just wanted to keep harm from herself. You might not like what she did and it might not even have been a good way to deal with the situation (it was actually really bad) but it came from the feeling of despair, which is a pretty substantial human feeling. Also she is by no means friends with Mi Rae. Mi Rae just is the first one to treat her like a person apart from her beauty because she realizes that Soo Ah has more or less has been forced into her role by a society that sees beauty as way more important than it should be, much like herself.
Sorry for the rant, but I think the themes of this manga are pretty interesting and deserve some thought.