Its got a custom rom installed just now, which is good as it will make fixing it easier. Swedish Snow RLS4 had some bugs in it, and there was a 4b released quite soon after, so this might be the problem. You could try updating to the latest version which is RLS7. If your wife wants to keep her apps, data (like saved game scores, app settings, etc.), and text messages, you'll need to back these things up first. All her contacts can be backed up to her Google account, so make sure that is set to sync them (in the Settings menu there is one about Accounts, choose that, click her Google account and make sure the boxes are ticked for things you want to sync).
For text messages, you can use an app like SMS Backup+ which will save them all and can restore them after updating to the new version.
For apps and their data, you can use the Titanium Backup app from the market. This will save them all to the sdcard, and can restore them afterwards.
Once you have backed up everything you want to keep, go to the Swedish Snow thread
, and download version 7. You want the Swedish-Snow-RLS7.zip one. Once you have downloaded it, use an md5sum checker (you can find ones for Windows on Google, or you can use AFV from the market and check it on the phone) and check the md5sum matches the one listed in the thread. If it does, copy the zip on to your sdcard.
You are now ready to update it. Make sure your battery is charged up, and turn your phone off. Hold the volume- button, and press the power button. Keep holding the volume- button, and you should see the green Android and then it should boot into ClockworkMod Recovery. Once you are here, you're going to wipe the phone and then flash the new version. Use the volume keys to navigate up and down, home to select an option, and back to go back. If you want to, you can make a full backup of the current install first. To do this, choose the "backup and restore" option and then "backup".
Now you need to use the "wipe date/factory reset" and "wipe cache" options on the first screen. Then go to "Mounts and Storage", and choose "format /system". Go back to the first screen, and choose the "install zip from sdcard" option, then the "choose zip from sdcard" option on the next screen. You'll now see a list of all the files on your sdcard. Navigate to the Swedish-Snow-RLS7.zip and choose that.
Wait while it installs it, and once its done, go back to the first screen and choose "reboot system now". Your phone should reboot into the new version. It might take a bit longer than usual, but that's normal. Once it loads up, you can restore the stuff you backed up. Signing into the Google account should sync the contacts back, and you can use the same apps that backed up the other stuff to restore it again.