Changing names?

So my stbad wants to change her name. She has a very uncommon name and wants to change it to a very common one and I don't know how I feel about it. She is 11 so on one hand I feel it has been her identity for so long and although i would def. change a baby's name an 11 year old is so different. Then I also see that is a new life for her and it is her choice I don't even know why she choose that name! I told her we would definitely keep her first name as her now middle name if we were to change it so she could go by it later in life if she chooses. Any advise? Anyone change names so late in life?