When you disinherit a child and don''t know if her name has been changed due to marriage or other will it be valid if you use name given at birth ?

Yes - you should just list it with the information that you.  For example, you want to say " I have three children.  Their names are John Smith, Mary Smith, and Jane Smith.  I am specifically disinheriting my daughter Jane Smith because I have had no relationship with her."  The reason you list that there are three children, and that you  are specifically disinheriting one of them, is so that there is no assumption that the attorney that drafted your will forgot to name one of your children.  If you just said you leave your estate to your children John Smith and Mary Smith, there might be an assumption that you simply forgot to name Jane Smith, not that you were disinheriting her.