I have made many, many floorcloths for a variety of areas, from high traffic kitchens to low traffic library areas. I have made small ones for tiny bathrooms, and large ones for covered decks and dining rooms. They can be decorative but they can also be functional. Make sure to seal it thoroughly with a flexible, non yellowing acrylic sealer. If you want to put it in a high traffic area such as a kitchen, you probably want to apply 8 to 10 coats. That will provide good protection from wear and dirt. It can be cleaned with a damp sponge. Depending on the weight of the canvas, you might need as many as 4 coats of gesso. Also, unless you are going to build a frame to hold it while you paint it, I would recommend that you start small (2 feet by 3 feet works well for many areas). With a bad back a small one that can be worked on at a work bench would be easier as well. What kind of paint did your daughter give you? I am curious to see what you do with the canvas. Floorcloths are a lot of fun.
Before I forget, when finished, the canvas will slide so you might want to put latex rug backing or a skid pad under it. Also, they do better on non carpeted floors.
Have fun! and Good Luck!