Either be self-employed and file schedule C with schedule SE, or get hired as an employee. You aren't going to be able to stop being audited if it looks suspicious, so the key is to be honest. She really needs to be working legitimately and reporting legitimate income.
Also note, that for purpose of earning social security credits, hiring a parent to work in your home will not work, because parents don't pay social security tax when they are hired for household employee work by their children. (Just a thought, you don't say but that is one situation that would fit the facts you describe.)
Also note, if she did not earn SS credits because she was a stay-at-home spouse or mother for a spouse who worked, she should be able to use her spouse's credits (or ex-spouse if they are divorced) to qualify for benefits.
