Does a girlfriend of only 5 months have the right to tell me that she will be attending all medical visits of my 20 year old son who is on my insurance and I am paying for the medical bills. She is a rude insecure little girl who always has t be number one in everything. I keep telling her that I am his mother and she can not take that away and that she does not need to compete with me. She says that she does not have to ask me if I mind her coming to his surgeries , etc. I understand that but why does she feel like she has the right to ask all the questions and leave me just sitting there like I am only there to pay for it

He's 20 years old, so I would say that it's up to HIM whether she has the right to be there. The person asking the questions should be your son, not his girlfriend OR his mother. Both of you need to back off a little and let him be the adult that he is.