In this situation, you will have to follow these instructions as if you were your mother. As long as you are "authorized" (by her) to receive this information, there's no problem.
Here are the detail instructions on how to get a duplicate copy online; it's not a bad as it looks, I just wanted to include everything so you don't show up in the wrong place:
The form that you can receive online at ssa.gov at your MySocialSecurity account is an exact duplicate of the one that comes in the mail. Let me walk you through what you need to do:
Try this link it is a more direct route:
Click on the Sign In or Create an Account
then either set up a "My Social Security" account or sign into your existing account.
Scroll to the bottom of the Terms of Service page and "agree" to their terms
then click on "Replacement Documents" at the top of the page.
Scroll down and click on this link:
View / Print / Save your Replacement 2016 SSA-1099/SSA-1042S
click "OK" to continue
Your 1099 Replacement Form should appear.
You can view it, save it, or print it; whatever you want.
Please note the the SSA is constantly upgrading their web pages, so it is possible that you might encounter slight variances in wording, etc. on the web pages.
Please remember to rate my response as that is the only way I will receive credit from the site, for assisting you today.
Thanks very much,