Often the Tucson Triumph dealer puts up bikes they can't sell on ebay at very good prices.
Click here for their current auctions. Their service department isn't quite up to standards IME, and it's the same with the other brands in the Tucson area. However, Sierra Vista, just outside FT Huachuca, has a good reputation from the people around here I've talked to. A friend of mine recently took his Harley to Sierra Vista for servicing, even though he bought the bike here. Honda owners I know also go to Sierra Vista instead of locally.
Of the Phoenix dealers, a poll on the Arizona Rat Pack site had results largely in favor of the Triumph Superstore @ 5640 North 7th Street Phoenix AZ 85014 • 602-864-1437. The place I bought my bike from used to get favorable recommendations, but the 2 quality techs no longer work there.
Of course your sisters best bet is to sell her bike and buy a slightly used one instead of trading in. Craigslist and Cycle Trader are 2 places to look for used bikes. I just found a Yamaha GTS1000 on craigslist locally that I'm buying.
I-10 in Phoenix and Tucson, plus in between is pretty bad. Through the rest of the state it's not too bad, and the speed limit outside Tucson and Phoenix is 75 mph so you can zip along at 80 mph without any worries from the law.