My daughter (19) and I are spending a few
days at the Fairmont Princess in Scottsdale.
My plan is to take a cab to the hotel. Do I
need to rent a car? Is there a shuttle or
bus system to get us to Scottsdale for
shopping or eating somewhere other than the
hotel? Anyone used the spa facilities at the
hotel? Shopping suggestions would be helpful
Thanks!

You simply MUST rent a car in Phoenix/Scottsdale (unless at a downtown convention).
Distances are long, virtually non-existent public transit.
The upside is that street/highway travel is easy and uncomplicated.
Princess is very easy to get to from the airport (but it's a long way).
Best shopping is Biltmore Fashion park at Camelback/24th, Scottsdale Fashion Square at Scottsdale Rd/Camelback, Fifth Avenue Shops in Old Scottsdale around 5th Ave/west of Scottsdale Rd, Borgata at 6100 Scottsdale Rd, El Pedregal at Scottsdale Rd/Carefree Hwy north of the Princess, Scottsdale Pavilions at Pima and Indian Bend.

You can catch a Super Shuttle to the Princess...when you leave the terminal, go out onto the median across from the exit and take the North Scottsdale shuttle.......after you get there you would be smart to rent a car...they may have a shuttle from the hotel and the concierge will fill you in on that...loads of restaurants and shopping close to the hotel at Bell and Frank Lloyd Wright, but clothes shopping would be best at Scottsdale Fashion Park, Scottsdale Rd. and Camelback......

Why would someone want to pay for a shuttle to and from the hotel, then pay extra to rent a car as soon as they get to the hotel?
The shuttle will cost as much as a day's car rental.

Rent a car. I made the mistake of using car service and it cost $50 each way from the airport to the Princess plus another $40 or so for a round trip into Scottsdale for dinner one night. I could have had a rental car for four or five days for the same price, and it would have been much more convenient too -- there are long waits for cabs/shuttles in a region where so few people use them.

You will enjoy the Fairmont Princess. And the restaurants are superb. We especially like La Hacienda. Also, you really need to rent a car and the best shopping is at the Biltmore Fashion Park. Have fun!