Besides cactus or something that grows in an arid environment, I would suggest cannas. They love sun and heat. As long as you keep them watered, they won't mind the heat. In fact, you really can't overwater cannas, unlike most other plants, so keep them watered. They will actually thrive in the heat, and you get beautiful foilage and flowers.

Try painting the containers white and mulching heavily. Or put water chestnuts and lily's in a bin with some fish. Containers on a deck have to be watered daily. If nothing grows you can always fall back on fake plants.

there are things you can add to the soil which will help. the best i have found is a product called watersorb (wholesale at watersorb.com. good for info too). it is an ammonia polymer similar to what is in diapers that absorbs 400 times its weight in water. it starts out like rock salt bit when wet looks and feels like jello. it slowly decomposes to ammonia and nitrogen (i have been told diapers are salt based and not good for gardening). local nurseries will usually have some variation of the stuff. it is pricey, but it takes very little. make sure it is well mixed in the soil. if used properly, it can cut watering down to a weekly event even in the summer. it is also helpful in the winter as it lowers the freezing temperature and keeps the humidity up in the soil. won't keep her from having to water, but it will buy about a week or two of neglect.

there are several nurseries here that specialize in water wise and native plants that require little moisture and can take the heat. some of my favorites are lavenders. the smell is reason enough, but they also do very well here. another is hens and chicks. there are several different kinds. mixed together in a strawberry pot or hanging basket they can be very interesting. the suffer a bit in cold dry winters, but pop right back with a little water in the spring. just need to have the dead leave pulled out and they look great again. many ornamental grasses are nice too and look beautiful in the late summer through winter when they go dormant and go to seed. many herbs are also fairly tolerant of Utah. sage does very well as does rosemary, thyme and basil. like the lavender, they add another dimension to the garden, smell.

good luck.

Last year, I got some large pots that look ceramic but are a double-walled plastic with about 1 1/2 inches of air space between the two walls. They seem to work quite well to insulate the roots from too much heat. Mine are on a deck that gets morning sun and afternoon shade. Still watered every 2-3 days. I grew Hibiscus moscheutos in mine and they worked quite well.