When an LPR returns from an international trip, can USCIS make her pay back Medicaid or Food Stamps that she or her children used before?
No. USCIS does not have the authority to ask immigrants to pay back these benefits. If an alien has received benefits improperly (e.g., if a person claims to be a resident of a state for purposes of eligibility when she is not a resident, or if she does not tell a caseworker about all of her income), it is up to the benefit-granting agency to request repayment, based on the rules governing that program. Typically a benefit-granting agency would only request repayment in situations involving fraud or overpayment, and it would follow its procedural rules involving notice to the individual and the right to appeal.