Weddingbee boards

I just received the contract for the harpist.  During our phone conversation, I asked her (like I have all of my vendors), what is the back-up plan if she is ill and cannot attend the wedding.  A note attached to the contract said the person she had in mind didn't want to commit to me, so that she could leave that date open if another wedding came up.  Should I look around and see if I can get another person to hold that date and use them "just in case"?

I wouldn't be so nervous if she was playing just the ceremony, but she is also playing the reception.  If something happens, we would have no music the entire time.  

Any advice?