Why are you recommending that she amend?  As far as I know, IRS doesn't pay you a finder's fee.  There is zero chance IRS will make an issue of this, unless someone reports her, and even then it's a waste of time for them to do $500 audits.  Did her husband file correctly, and show her SSN on his return?  So they already have evidence that she's married, if they want to pursue her.  

How closely did you look for other errors that the prepare made, that might have cost her $500?