US Airways Dividend Miles (Pre-FlightFund Merger) - Pet Question: UA-purchased, US-operated non-codeshare

So for an upcoming trip, my wife and I want to bring my Papillon with us to visit some family. The tickets are most likely going to be purchased through UA, with UA on the outbound and US on the return trip. I know how to pay UA for a carry-on pet after making a reservation, but what about US?

You'll pay the $100 fee at the ticket counter or gate before your flight. You should call US beforehand and let them know that you will be bringing your pup onboard. I believe there is a 2 pet limit in Y, 1 in F on each flight. Here is the link from usairways.com: http://www.usairways.com/customers/travel_policies/pets/