Singing

A family friend agreed to sing the song I am going to walk down the aisle too and her husband was going to play the keyboard.  Earlier part of this month she told me not to count on her husband because he has been sick.  I told her no big deal I would have my DJ play the instrumental version of the song and she could sing to that.  Then I started thinking and I asked her did she still wanted to sing.  Who knows she may not make it that day due to her husband's illness.  She stated she would talk it over with him and let me know.  So I emailed her last night asking her again since we are 8 weeks away.  She stated she had to leave work early today because her husband was sick.  She wanted to be fair and let me go ahead and let someone else sing.  She apologized and stated she was crying while she was typing the message.  My FI has a co-worker that sings.  I told my aunt about it and she thought it would be weird letting someone sing that we don't have a relationship with.  Now the lady that was original is going to sing is my aunts best friend and is like family to me.  My aunt stated maybe we should play it by ear and if her friend can sing then great and if she can't I will just walk to the music on CD just like my wedding party will be.  My FI is stating why can't we get my co-worker to sing.  Now I told him if we did of course I would have to hear her sing first.  Now I just don't know what we should do.  I would love for the family friend to sing because believe me she can blow, but if my FI co-worker can sing why couldn't we go with her.  Do you think it's weird to have someone you have no connection with sing at your wedding.  I know when you select people for your wedding it's people you normally have a connection with.