From what I've read (haven't done yet) you need to cook poke in several, or at least a couple, changes of water to get the poison out. So you would need to do this before canning. I would think that they would be complete mush by the time they were canned, after all that cooking, wouldn't they?
Did Grandma blanch them before freezing them? I'd precook them, then freeze. If you don't blanch, they break down. Blanching destroys the enzymes that slowly "digest" them over time, even in the freezer.