She later ran into problem with Niagara Falls USPS ,the postal clerk told her they cant accept her package as her return address is Canada .
It makes sense,if the package has to be returned,USPS would have to turn the package over to Canadian post office
Easily solved - if needed - with a postal box rental in US
For affordable shipping from California to the USA, consider USPS, UPS, and FedEx. USPS is often cheapest for small, light items. UPS and FedEx can be more competitive for larger or heavier shipments.