Can't upgrade iOS 4.3.3 to iOS 5.1 on iPad

Question

I'm trying to help a technophobe friend update her iPad from 4.3.3 to 5.1. She's done no upgrades to her iOS since getting her iPad. I've done each of mine seamlessly. I am completely perplexed and haven't found an answer to our dilemma since we embarked on this quest. To make it more challenging for me, she has a PC so I'm in foreign territory working on her computer. She also hasn't turned on her laptop in the year she's had her iPad so we had to update iTunes. That part went fine.
We ended up syncing her iPad about three times so all of her apps and music are up to date on the PC and the iPad. The update of the of the iOS appeared to work each time. It took the 89 minutes it predicted at the start. The update message says it's 5.1 and it says it will install after downloading. We have now gone through this process FOUR times. That's a lot of hours for nothing. The last time we actually babysat the process. It was as exciting as watching paint dry. It appeared to flow fine concluded in front of our eyes. The ipad switched to the wallpaper screen and had a small tone. The Apple came back to the top iTunes banner. Then NOTHING. I checked Settings>General>About and it still said Version 4.3.3. We uncounted the iPad, turned it off and powered it up again and it is still on 4.3.3.
What are we doing wrong?
Her iPad is the Verizon model and I saw in one thread that said there are three varieties of upgrades but I don't know how to verify the right one is downloading from iTunes. I would hope the iTunes connection can detect which version is needed.
I also found on the Apple website the list of four upgrades she neglected before 5.1. It indicates those older updates are available in iTunes but I can't figure out where to get to them. The Upgrade button goes right to the 5.1 version. I'm wondering if there are components in those incremental updates that she needs before 5.1 will work, or does 5.1 install everything she's missed along the way?
Any help or insight on this frustrating situation will be appreciated.

Answer 1

I solved this problem with detective work and hints from another discussion thread. I detailed my solution here on the 3 April 2012 entry of the following thread:
iOS 5.1 won't upgrade my iPod & iPad 2 on my newer mac, but it will install perfectly to my sisters same model iPod using an old windows laptop in the same internet connection in the same house
   Apr 3, 2012 10:23 AM    (in response to MacLoyal)
https://discussions.apple.com/thread/3787478?start=45&tstart=0
Perhaps someone else is struggling with the same roadblock. You cannot jump from 4.3.3 to 5.0 or beyond over a wireless connection. You must be plugged in with an ethernet connection to your internet. After 5.0 you can update OTA, translation Over The Air.
I don't know if the OP (Original Poster) was trying to do it wirelessly with a Mac, but in my case it had nothing to do with being on a PC or Mac (with the exception of me being in foreign territory in her house and on her PC - MacLoyal, I am) and everything to do with not having a wired connection to the net.