Dear Dawndarcy, hello
Your daughter seems to have soft tissue injury
resulting in inflammation in that area. Inflammation results in some steps to heal the wound.Shin has thin skin so pain appears more. So, you should not worry and just take care of the cleaniness of the wound and apply some antiseptic cream over the bruise
Since her age is 4 years I hope that she is fully vaccinated for tetanus
I hope this is of help to you.