This is a two year old question.
Her side of the story could very well be the truth - dad's made no effort to contact him. It's not like that never happens.
But regardless unless there is to be an adoption taking place taking away parental right's does nothing for the child at all, and an 11 year old has a lot of years ahead of him to deal with things like that themselves.
My advice would be: If he did not choose to be a dad in the first place opt out of child support, that's a rather simple process that doesn't strip right's or obligations later on.
If he did choose to be a dad find out what his life is like now, talk to each other like adults, seek him out for your kid etc. You talked about back child support, maybe his financial means have changed and he might be too embarrassed to seek out contact.
I know I'm guilty of the life experience thing here a lot, but my daughters dad is very "shy" and if I hadn't heard about his layoff in the news when the kids were little he probably would have never brought it up to me and sunk into child support debt while not seeing the kids because of guilt. Regardless of not getting along this article reeks of not being parents together and that really is the worst possible option. Caregiving and finances regarding your children are both needed.