Is it necessary for DORIS to change her name to an Islamic one when converting to marry your brother?

My brother wants to marry a non-Muslim (Christian) girl, when we told her that she needs to convert to Islam wholeheartedly in order to marry my brother which she agreed but she does not want to change her name from DORIS to an Islamic name. She says that she will keep her name and gave us proof from internet saying it is not necessary to change your name if you are converting to Islam. In spite of our repeated efforts brother does not understand. Kindly advise us whether it is necessary to change name, in this case from her name DORIS to an Islamic name.