User is receiving error notification after amending PO to change requester from terminated employee

We have a user who is working with a PO and is trying to update the requester from a recently terminated employee to an employee that is active. The user amended the PO to change the requester from terminated employee to active employee, then she amended the order again to add quantity and amount on the lines to match the term of the agreement. When she tries to submit the change, she's receiving the error notification below:

Process Name: Purchasing Document Approval

Issue Type: BPEL_TASK_30082

Issue Description: The StandardPOBetwen100001and15000Dollars rule in the PreApprovalHierarchyRules rule set failed because a supervisor does not exist for terminated.employee@example.com