Re: Questions from a new user
The difference between the 3G and the newer iPhones is enough that your intended purpose won't really be satisfied.
Being held back to an older iOS version prevents you from using many of the features. Rdiddy already covered a couple if those features.
Something else you might consider is looking at an iPod touch or used iPad. You can find either of those items moderately priced. If you have kids, the iPod touch might provide useful as more than an introduction to apple products. If you do take this option, be sure to check the model number on the back to find out the generation and search to see that it will update to iOS 5 or newer. This will give you the most similar experience to the new iPhones. If you happened to be in the tablet market, using your iPad would be far more comparable to a new iPhone than the 3G.
In addition to default features that only exist on modern iOS versions, many apps will no longer be supported or installable on older iOS versions. You won't truly get the experience you're looking to provide when she gets the phone.
Another option is to trust your tech abilities. Many of the restrictions apple imposes are meant to target non-tech users. Apple TV use is simply putting the phone and appletv on the same network. To send your phone to the appletv you'll click on the little up arrow that shows up on media. iCloud is mostly signing in and choosing the options from your settings menu. You should be able to easily help guide her through these, if she even needs help, without having worked with apple products in the past.
Finding the carrier might be a mess. That will be more of a headache than helping your wife later.
Restoring to get rid of the jailbreak won't change anything within the apple ecosystem. It'll just add more headache.