Dell - I think Walmart or some of the other stores sell pop-up laundry nets like the one in this photo:
They make a great cage! Or you can possibly purchase an actual butterfly cage like this one. I have 4 of these and love them. I soak them in the tub in water with a little bleach between uses. (Helps prevent diseases that pass around among the Monarchs.)
This is what the actual butterfly cages look like:
See the "Large Pop-Up Pavillion pops open to form a 2 Foot tall screened-in cylindrical enclosure with a 14 inch diameter." You can use these over and over again. You only need 1 cage to raise a few butterflies of the same species. You want one that is at least 2 foot tall to accommodate any tall plants. It gives the butterflies lots of run to fly around, too!
Something else you could do for your mother ... raise some in these cages. Get some host plant seeds or plants and grow them in small pots that you can place right inside a cage. Let your mom watch them grow from a small egg, to a caterpillar, to a chrysalis, and then to a butterfly! People of all ages enjoy that! And then get her to the back door and let her release them outside the door!