There is no time limit on pressing charges for Sexual Abuse. You should first report it to the police. It is recommended that this is done in person. Your daughter can bring you or anyone else she wishes with her for support when she makes her statement. She can ask to speak with a male or female officer, depending on what makes her most comfortable. The experience may be very upsetting, and she can request a break at any time.
It's vital to your daughter's well-being that she sees either a trauma therapist (preferably one with a cognitive-behavioral approach, as they teach you how to cope with not just the memory) or a Counselor (a relatively new addition to the psychological field, but very effective)
Your daughter cannot personally press charges, since sexual abuse is considered a crime against the State (which carries harsher penalties), and would be considered a "witness" to the crime. Criminal charges can take up to two years to go to court. Since criminal charges require "proof beyond a reasonable doubt", you may want to discuss with an attorney the possibility of charging him with multiple counts of child abuse since this man also sexually harassed other children in your family.
These cases are always harder to prove later in life, but I do believe that there is justice for your daughter. Trauma therapists/counselors are very familiar with this territory, and can help guide your daughter through the process. I firmly believe you should prosecute this matter. One in three women will be sexually assaulted, statistically, and that's only of the assaults that get reported.
I'm so sorry for what your daughter had to go through, but please know that there is hope