I did a search and found this on the royal mail site which mentions some changes in the Greek system of customs:
Start date:June 2017
End date: Ongoing
Greece Post has informed us that since the end of June 2017, it will be acting as a direct representative of customs authorities. It has been applying new customs procedures on both International and domestic mail collection and delivery involving new information systems to facilitate and improve customs clearance time.
During this initial, adjustment period, there may be some delays in the handling of inbound postal dispatches and delivery of items subject to customs clearance.
I realise the above is inbound, but RM are obviously looking at it from the point of view of sending items there. It may be that there is a similar situation in reverse with items going out.
In terms of postage out, it wouldn't affect post to the UK because we're all still in the custom union. So PKW, it may not have impacted on your parcel for that reason, but going to Canada, it might relate to this. 2 months seems a bit extreme though...maybe she had another sale which had that problem and that's why the seller has raised it now.