If BC does block Alberta's oil or fails to stop protesters, that will set a definite precedent. One that Notley can use.
 
Its simple. She can prevent the shipments of all products leaving BC, by rail or truck, heading east. Likewise she can prevent the shipment of all products heading to BC from the east.
 
Its a bit radical I know. But, how's this. BC doesn't want Alberta's oil? Good enough. Shut off the existing Trans-Mountain pipeline.  Once the lower mainland runs out of gasoline, diesel and jet fuel there will be a change in attitude. Think the Washington State refineries can supply the lower mainland? Ever hear about that Chevron refinery in Burnaby? The one at the BC end of Trans-Mountain?