You are posting the email address in the clear so it's a target. Only Yahoo can reset the password and if you don't remember the details then you should never get the address back. I'm unsure why this is not clear to you so my reply is to clarify the issues.
1. Posting an address in the clear is a very bad idea.
2. If you don't have the answers to the security questions, then it's not your email account. Even if it was, it is not yours anymore.
Time to get a new account, and tell Mom to block the old address.