Sorry to hear about your granddaughters iPhone 5C . I would say anytime someone’s screen pops out of their device it is definitely not a good thing. I would advise you to either go to your nearest Rogers corporate store or contact customer service to see whether you can have the device looked at (also to see if it is covered under warranty).
If by any chance this is not covered under your warranty, I know Apple is really good at assisting in situations such as these. Just curious, could by any chance this be some sort of case or screen cover?
Let us know what the outcome is, or if you would like I could have someone reach out to you via private message.
This has happened to me both on the Iphone 3gs and on my iphone 5. This happens because the battery itself starts to bubble and it pops off the screen. On the iphone 3gs, it bent the motherboard so replacing the battery was useless unless I replaced the motherboard. However on my iphone 5, i managed to get a new replacement battery within a week and now there is no problem. Because she popped the screen back in, see if there is a bulge starting to happen (left hand side), and also if you tap on the screen you see a change in colour/colour wave appear... if so then it is the battery startng to bubble (happens if you over charge, or if you use it while charging)
If that happens again or to anyone else take it to Apple and have them check it out / exchange it like u did. The battery is NOT supposed to do that at all. That can cause the battery to explode and cause severe injury to ur self or cause a fire. I have over charged many devices and never happened to me thankfully but always make sure u don't overcharge the device and make sure the device is cool and not hot.