I forgot my Apple ID EMAIL, not my Apple ID.

How do I find my email?

My mother set up an Apple ID account about 7 years ago when she bought me a nano. I was way too young to know how to set up an account so she did it for me. Now she doesn't remember the email she used.

We do know the Apple ID and password, but we don't know the email address used. I updated my iPhone today and now I need to input my email address. (I can't use iCloud either.)