I love your grandma's idea! I am not a seamstress, but if it helps at all, the snake cozys I have had such great success with are made from a material called 'minky'. I think the circular entrance may just be an embroidery hoop, since those come in a variety of sizes and they are fairly flexible. They look like they'd be pretty easy to make, though friends of mine who are into crafting have mentioned that 'minky' can be challenging to work with since it's so soft/velvety. I've been meaning to post about the snake cozys here. I originally thought they sounded silly, but the nearly unanimous and very enthusiastic response to them by almost all of my snakes has convinced me they are really worth having around for anyone working with nervous snakes or anyone interested in enrichment.