She should check and re-work both her estimate and her actual division. When an estimate turns out to be wrong by that much, either the estimate or the division is way wrong, and there's a good chance they both are.
After you make an estimate and then solve your problem, you compare your estimate to the answer you got. If everything is worked correctly, your estimate and your actual answer should be close.
In this case, her estimate was 120 and her actual answer was 83. These are not close in value, so there is either an error in her estimate, in her division work, or possibly both. To verify where the mistake is, she should rework both the estimate and the division.
