Q: Facetime problem

Hi

Here is my problem,in the Facebook settings on my iPad where it says 'You can be reached by Facetime at" it has my email address which is my Apple ID and the phone number is my wifes phone number.

But her number is not associated with my Apple account.

It is very annoying because I can't facetime her when she is at work.

How can I exchange her phone number for mine ?

thanks