I figured that would be the easy thing to do but in that case I have no real argument for her to pick the windows phone over the iPhone besides the price.
Well, that depends on the device. With the 8X, it's not even cheaper. Verizon offers the 16 GB model for $200, so it's the same as the iPhone. My sister's on Verizon as well, and she chose the Lumia 822. Nokia offers exclusive apps on its devices, and they really do make the difference. Tell her if she gets the Lumia 822 (which my sister got for $150, with a $50 mail-in rebate than I need to remind her to send in), she would get:
--microSD slot: The Lumia 8xx line has microSD support, which the 920, HTC 8X, and iPhones do not. The 820 and 810 come with 8 GB of storage, but the 822 comes with 16 GB and the expandable storage, so it's the best of both worlds on that front.
--Words with Friends and Draw Something: These are on all Windows Phone (if she likes the games), but only on Nokia can you get free, ad-supported versions (the paid ones are $2.99 each). I installed them but haven't played them myself, but it's nice that Nokia's working hard to get apps.
--Nokia apps: These include Nokia Drive (voice-enabled, turn-by-turn directions), Nokia City Lens (neat function to show off and find places to go in a new city), and more.
--Nokia Music: This is one of the "and more" apps, but it's so great that I thought I should mention it alone. Free, ad-free streaming. 4 playlists can be downloaded and used offline, so no data consumption. That basically makes it the best music streaming option on smartphones.
--NFC: Not extremely useful, but Apple has no NFC-capable device, so if it becomes more popular, she'd be out in the cold using it.
Xbox LIVE: If she uses it already (I know most girls don't, haha), she'll be able to bring her gamertag and friends list, while being able to earn achievements on Xbox-enabled Windows Phone games.
There is a lot that Windows Phone offers, but to get the most out of it, you really kind of have to go with Nokia. The HTC 8X might have the colors and build and resolution over the 822, but the apps the 822 offers are just too good to give up, in my opinion. Nokia Music has essentially made me stop using my Zune HD altogether, which is bittersweet (love the app, but hate that I don't use my Zune, haha).