You cannot downgrade to 4.2 without SHSH blobs and the only way you could possibly have them is if the previous owner (if the phone was not brand new) of the phone jailbroken it and saved its blobs. Even in old bootrom 3GS, SHSH blobs are still required.
DO NOT EVER FOLLOW ANY TUTORIALS SAYING YOU CAN DOWNGRADE W/O SHSH BLOBS. It will royally f-up your phone. Tho it is possible, there is not one single benefit from it. Causes nothing but problems. You have been warned.
So my suggestion for you is to freshly restore your wife's phone to 5.0.1. DO NOT restore from backup. If you restore from backup then whatever is causing the phones problems in the first place will be uploaded back to your phone again, thus........defeating the purpose of restore in the first place.
You will have to restore, and setup as new and redownload all your apps. (unless you transferred them to iTunes in which case you can just transfer them to the phone from there)
I know it sucks, but it is the only way to r really resolve any problems. (especially if the problem persisted after a restore)
However you can transfer all music and apps by right clicking on your device on the left side panel of iTunes and then clicking "transfer purchases". Then all music and apps will be backed up to iTunes.
So all your apps ad music will be saved to iTunes, but all other data, settings, accounts, contacts must be reconfigured.
And what I personally like to do to save my contacts w/o iTunes cuz......well I hate dealing with iTunes with anything besides music and apps.
On your phone, open the app store and buy and download an app called "contacts backup over dropbox". Tho you would have to make a dropbox account. Which is nothing less then a great idea. Dropbox is awesome, free, and worth having.
Once you made your dropbox account, open that app, sign in and tap "backup" (obviously do this before restoring your wife's phone.lol). Then once the phone is fully restored, install contacts backup over Dropbox again, open it, sign in, and tap restore. Quite impressive how fast the process is. Literally a few seconds and all your contacts are back in your phone just as they were when you backed it up.
And I'm not usually a promoter of anything or anything but Dropbox gives you 2 GB of space to store files of any kind for access on the web at any place, any time, provided you're Connected to the internet with whatever machine/device Your using. Oh and can also earn more space by having others sign up for dropbox with your own personal link provided by Dropbox. In fact I was going to post my link here but I don't think that's aloud in this type of forum. But either way you should get a Dropbox account and download the contacts app because you will not regret it. this I promise you.
Plus I believe iTunes has to restore from backup to put your contacts back any way, but not sure in that 100%.
But what I do know is restoring from backup is the best way to resolve problems. I never ever restore from a backup. I always setup as new.
I just use AppBackup from Cydia for the data in my apps, and contacts backup over dropbox to put my contacts back. I save my photos rite from my phone by uploading them to the Dropbox app, which is free. Then, When I'm done restoring I just open the dropbox app and take screen shots of the photos I saved there from my phone before I restored. (don't really like the way photo stream works, Dropbox does this much better)
But for email accounts.......well I don't find it too much of a hassle to just re-add them my self manually.
However if just doing a fresh restore as new does not fix the problem, then it must simply be a hardware problem, and would suggest you take to an Apple store. And tell them everything you've done.
Good luck and I hope this works for your wife's iPhone 3GS.
