Can a beneficiary tell Social Security to stop sending them SSDI?

My cousin has been receiving SSDI for a while, and starting working several months ago. She isn't sure how many months she went over the $620 monthly earnings limit, but she is sure it is at least 6. She is making good money now, and would like to avoid an overpayment, since it doesn't appear that SSA updates their records in a timely manner. What should she do?