Also sorry to hear the news of your wifes injury. There are two companies that HAL and the other lines use for all medical supply rentals...
Cruise Ship Assist 866-889-8099
Care Vacation 877-478-7827
These two companies provide the rental, coordinate the delivery to/pick up at the pier and notification of the cruiseline. They make the process easy. One thing you'll also want to do though, the delivery won't put the chair where you can access it when you arrive at the pier for the line at embark. You'll need to contact your T/A and request what they call pier assist. They have complimentary wheelchairs for embark/disembark upon request. With HAL there may be a wait for one. There are many pier assist requests with this line on Alaska sailings. They only have a couple so you may have a long delay at the curb or transfer van until one is free. So arrive early if possible.