It's ok that you have questions. It can be a scary prospect to face your inner child.
Little Sue may have never received the love, attention and protection she needed to feel emotionally safe. She was exposed to abuse and not cared for as she should have been. So she develop ways to cope the best she could. But coping only goes so far so she was emotionally traumatized by what she went through. By working with her, you can provide her with the love, care and attention she deserved. You basically take the place of a parent or caregiver that she should have had to provide her with what she needed. This helps heal you "from the inside out" so to speak.
By working with your inner child, you can explore why you did not like her, which could have been a reaction you picked up from those around you. Children tend to see things much differently than adults. If someone dislikes you as a child and abuses you, your reasoning becomes that everything is your fault and you hate yourself. By working on your inner child, you can learn to love her and therefore love yourself.
A picture of yourself during the worst of your trauma might help, but anytime you feel is significant is good too.
It's ok to be frightened by how you feel. Therapy is work and often it can feel overwhelming. But you have support and people who care about you now, and you are an adult and have control. This will not hurt you. It may bring out feelings that feel overwhelming, but the process is good. It is healing a wound. It takes time and patience. But in the end, you will feel much better.