In a prospective study of PFPS, the precipitating factors were found to be tight quads and tight calves. If your hammies are "over stretched" (not sure what you mean here

) or very extensible then you may have stiff or short quads (especially rectus femoris).
You may also have some glute medius (and most likely glute max) weakness or limited internal hip rotation. All of these have been identified in other studies as influences on PFPS.
Short arc quads and the like are ISOs for the quads. Some may present with weak VMOs and that is often prescribed and an "isolation" exercise (Not true). The VMO can undergo some stretch weakness depending on how long mechanics and sypmtoms have been apparent.
Bill