Size 16 Narrow width women's slippers in Canada
You can get great deals on large size shoes at Amazon with a bit of patience. Their own Amazon Essentials range up to size 15 US is well worth a look with fashionable styles at great prices. The women's shoes department goes right up to 16 US, although many of the largest sizes will either be Chinese brands or unisex.
Specialist large size shoe store in Quebec also selling online to Canada ($10 flat rate shipping) with a wide range of women's shoes in sizes 10 to 15 US, with selected fantasy styles up to size 17 US. Large selection of brands and styles. They even do rain boots, slippers and socks. They are happy to advise on the right size for each style if you send them your foot measurements before ordering or during checkout. You can also visit their shop in Rue St-Hubert, Montreal. Website is in french.