Hi Ceejay, I agree with Kaz, you can grow almost everything depending on container size. You just have to have good fertility since everything will be in containers and plants will use up the available nutrients quickly.
In addition to his list, you can grow most stone fruits with regular pruning, especially those that fruit on new or one year old wood. Figs, eugenias, jaboticabas, blueberries, strawberries at the base of other plants, cattley guava, wax jambu, and other guava species. Pineapple guavas are really easy, grow quickly and look good all year with really tasty fruit from named cultivars as well as tasty flower petals.
I add edible flowering plants like nasturtiums and violas to the base of containers, as well as chives, arugula, parsley and other herbs. These all make salads more interesting and add beauty to the containers without taking up extra space. They will also bring in lots of pollinators and beneficial insects when they bloom. Daylily plants are also bullet proof, and the flowers can be used in any recipe calling for squash blossoms. The simpler varieties taste better, the highly ruffled ornamental varieties are not as tasty.
I could go on and on, but I would suggest, planting fruits that she really likes and add flowers for beauty, so she'll be motivated to take care of the plants. Good luck!
Janet