How to remove a jailbreak

Having trouble updating my girlfriend's iPhone 4 to iOS 5. It is jailbroken. We wish to take the jailbreak off because I told her that it is not a good feature at all and it voids her warranty. She didn't even ask for her iphone to be jailbroken, the guy at the kiosk who sold her the phone did it anyways because HE likes his stuff jailbroken. She wants it removed as she didn't even know what it was. I told her that the Apple store can possibly remove it if she explains that she never asked for it to be jailbroken in the first place. I tried updating her iPhone remotely from where I am in California, as she is in Thailand, but it goes through the process of backing up, the progress bar hardly moves at all, then it just stops and it never updates. The updated software downloaded fine, but it just will not update. Could it be because of the jailbreak? How do you restore it to factory settings and remove the jailbreak before updating to iOS 5? Is that even necessary, or should she be able to update to iOS 5, thus finally removing that jailbreak garbage? Thank you for anyone who is able to help. She has synced her iPhone once, well, I did, via remotely, and it backed up and synced fine, but when it goes through the process of updating to iOS 5, that's when we run into some issues. Will Apple be lenient with her because she never asked for it to be jailbroken nor understood what the guy was telling her? She wants it off as she doesn't nor ever wants to use it.