When I went to the apple store a worker said I could merge two apple ID's. How can I do this?

My sister was the first person to get an apple product before anyone else so she created her own Apple ID. Then other members in my family including myself, received apple products and made a family Apple ID for all of us to use. My sister now uses the family account so she has forgotten her old password, but most song purchases were made on her old account so they are not authorized for other computers and obviously she doesn't know her password to authorize them and no longer has access to the email she used. Can we please merge her old account to our family one so that it is all under one ID?