It is unusual for international students to receive refunds on a return.  Did she have taxes withheld in full on income that should have been subject to concession rate(s) or exemption by treaty?  If so, she should make sure she submit the relevant certifications to the payer/withholding agents so that this does not recur.

In terms of the difference in refund, the IRS may impose interest charges on the amount she needs to return.  On the 1040X, just show the difference without including any interest.  Do, however, let the client know that the IRS may send her a notice for interest due on the balance shown on the return.