Do i have a right to challenge my daughter in law for access to my grandchild?

My son's g/f has stopped me from seeing their baby. She claims it is because I challenged a group of rowdy young men who were acting in an anti-social manner outside my house at 3am last year. However, my son has said that his g/f received news from his cousin that I am not to be trusted with children. There is absolutely no grounds for this accusation and it is causing a lot of trouble, not just for me, but for my son too. Do i have grounds to legally challenge my son's girlfriend?