McGuigan used a box cutter on Jan. 20 to rob the convenience store in Charlottetown.
Provincial Court Judge John Douglas set June 19 for sentencing McGuigan. Douglas ordered a full pre-sentence report.
McGuigan, daughter of long-time Deputy Chief Gary McGuigan of Charlottetown Police Services, does not have a prior criminal record.
The RCMP reviewed the Charlottetown police investigation into the robbery and determined there was no outside influence, special treatment or favouritism.