It is never too late to get help for your child. The optimal time to get help is as soon as you realize there is a serious problem.  Cutting is a serious problem, and a growing cultural problem among teens, especially young girls.  Here are some ideas and guidelines that may help you deal with this issue.
 
First, finding out that your daughter is engaging in self-injury is alarming. It is important not to take on personal blame, but to take this problem seriously. From what you say in your question, it sounds like the pictures your daughter sent are the tip of an iceberg, under which cutting is another layer. Behaviors like these almost always give a signal that the person is stressed, and is hurting. Young adolescents often act out their stress and emotional upsets by turning to cutting and other forms of self-injurious behaviors (SIB's).
 
Second, the good news is that your daughter told you she was cutting.
SIB's are often done in secrecy, and kids are not always able to let the adults in when confronted. The reasons that your daughter is having "bad days" at home need to be understood; but whatever the causes are, even though she is casting blame, they are not your fault. They may be  deeper than even your daughter herself can understand. As irrational as it may seem, in many cases, the SIB is an attempt to solve a problem of psychic pain that the person is unable to manage emotionally.
 
Third, your daughter needs treatment, and there are professionals trained to treat those who injure themselves. Start with your daughter's doctor, and ask who in your locality is trained to treat SIB's in young teens. While it does not help to take on guilt, it is important to take responsibility for getting your child to the proper mental health provider; and to also be prepared that treatment may involve yourself and other family members. While SIB's are not due to parental fault,  there may be stress in the family that is affecting the person who is cutting. Any familial stresses must be addressed if the person is to fully recover.
 
It is normal for you to be afraid that you will lose your daughter; however, the reality is that despite any anger or blame she is casting, she needs her parent(s) more than ever to recover from this problem.  There is every reason to hope that by getting her the proper treatment as soon as you can, your daughter will be able to find more effective coping strategies, and the entire family unit will benefit.
 
Bette J. Freedson, LICSW, LCSW, CGP