As humans, we tend to  look for someone or something to blame, but blaming oneself after being abused is more common than you would think. An important part of the Grooming process of an abuser is to make the victim feel that he/she wanted it to happen (because he/she didn't do anything to stop it). Remember to be very kind towards whomever had experienced this.

It’s okay to have complex feelings for a person who has harassed or abused someone you care for. However, abuse is never the abused person’s fault. It is always the fault of the abuser, who takes advantage of a victim’s trust to hurt them. Victims can’t change abusers, and it’s not healthy or safe to try.
You can, however, care for yourself, for the person who experienced abuse and decide what all need to be happy, healthy, and to live free of emotional, sexual, and physical violence.
https://www.talkspace.com/blog/dealing-with-complicated-feelings-around-abusers/

Some experts say that it is easier to change the way one thinks, than changing the way one feels. So although it is difficult to understand that none could stop the abuse the way it happened, the victim may still feel that it was his/her fault.
It often takes time for changes in the feelings to catch up with changes in the way of thinking.

Forgiveness is not about denial. Self-forgiveness is about recognizing that something bad happened but that it was not the victim's fault. 

Victims should never have to forgive themselves because of the abuse. The abuse is always the responsibility of the abuser. However, victims do have to forgive themselves for the negative choices they may have made because they were abused. This could be destructive relationships, addiction problems or negative behaviour patterns.

Letting go of the angry feelings they may be holding against themselves and getting support to deal with difficult issues is a way of forgiving and caring. 

Forgiveness is a much more complex process than many people think it is. It takes time. Getting in touch with the pain, anger, grief and loss is all part of the process of forgiveness. All these stages are not to be rushed. 

Self-Forgiveness is a journey of many steps, each of which can be extremely difficult, all of which are to be taken carefully, thoughtfully, and with deep reflection. 

Something important to mention is that forgiveness has nothing to do with forgetting or being re-abused.