Brittany, There is a great booklet you can pick up at the library and sometimes at a nursery, it's free, I've seen it at Bakers. Landscape Plants for the Arizona Desert. I have a shamel ash and it needs 30 gallons of water per week in summer. I'm surprised Susie would suggest a water intensive plant.
Here's some ideas from my copy of the booklet:
leather leaf acacia (evergreen) - to 10' - slow to moderate growth
anacacho orchid tree (semi-evergreen) - shrub-like to about 8' - slow to moderate growth
cascalote - (evergreen) to 15' slow to moderate growth
foothills palo verde (evergreen) to 15' slow grower
mastic tree (evergreen) - to 15' slow grower
mexican buckeye (deciduous) shrub-like slow grower
HTH - I browsed by tree size only, looking for any under 15'
