Uncle touching niece with lust

I have a question regarding the validity of my friends nikah. My friends uncle touched my friend with lust when she was almost 10 or 12 years old. Afterwards he didnt do such things with her. At the time of nikah, my freind chose her uncle as the wali or as we say, the wakeel of the nikah from her side. Now she has four children and she is worried if her nikah is valid or not.