It won’t affect your credit, unless she runs huge bills
Adding your mother to your Amax account as an authorized user won’t affect your credit, unless she runs up huge bills that you can’t pay. Since you are the primary card holder, it’s you that would be completely responsible for paying the bills.
If you’re doing this to help your mother build credit – forget about it. Piggybacking with authorized user accounts only count in the Fico score for spouses and kids, but not parent (See credit-piggybacking.html for more information),
If you want to help her re-establish good credit, help her get a secured card in her name and make sure she pays on time.