My guess is that her weather will be a lot like the weather here with lots of fine, bright, warm days and quite a few wickedly chilly nights. She's a little south of where we are here, and almost 2000 ft higher. There are mountains around Prescott that are the same height. And they get a lot of snow when we get rain. In any case, it is not uncommon for fine daytime weather to lure a plant out of dormancy and then for a hard frost to whack it hard. Then there is the fact that the ground is only ever moist when the roses are dormant. So she'd have to be committed to watering it regularly for some time. Of course the fact that there is no soil to speak of can be a real detriment. I'm not telling you anything you don't already know.
In any case, I kill a lot of plants, too. I can't tell you how often I've thought of just declaring pigweed a decorative garden plant.
I have noticed that Le Reve, owing to its close relationship to R foetida, no doubt, appears to sail through all sorts of bad weather - blistering heat, yo-yo temperatures, dryness, and so on. I know you didn't have this in mind, but maybe one of those two cultivars would be a good starter rose for your mom. The roses may not look like much individually, but when you've spotted a 35 ft tall Le Reve in full bloom from 200 ft away, it's a sight hard to forget.
