Unless things have changed recently, the way I would do it would be to ask for a pat down instead of going through the metal detector. When you meet the screener that is going to do the pat down, explain the problem. If she cannot remove the shoes because she cannot take them off herself, the screener should take them off for her. And then after the shoes and your mother are screened, the screener should put the shoes back on for her. I've done it a thousand times for women for various reasons. And I never minded doing it, I'm only too glad to help. If there is a reason your mother shouldn't have the shoes off at all, I would explain that to the screener and see what the options are. They may only swipe the shoes and that may be enough. If it becomes an issue that they cannot be taken off for some reason, ask for a supervisor. If the issue is not resolved by them, ask for the Federal Screening Manager. Take care.