The first thing you have to understand is that the shipping cost cannot be part of a Best Offer.
If you make an offer on an item, you can offer half of the asking price (and frankly I'm amazed that the seller didn't ignore and Block you) but you are accepting the shipping price as given.
So when you made your extremely low offer, the seller was accepting it at your Canadian address and with the Canadian shipping fee.
When you changed your address, she probably looked at her bottom line and said.... well, the mods would probably censor it.
The Best Offer failed.
Move on.