I think the previous unlock method you used was temporary unlock solution that means if you update or restore your iPhone then it will be locked again. To avoid this you need to unlock your iPhone permanently .To permanently unlock your daughter's iPhone 3G use remote unlock service . Using remote unlock method is safe and it will unlock the device permanently(It will never get locked again) . It doesn't even require jailbreak. This remote unlock works on all (GSM iPhones) iOS and base band versions. You can get this service from
http://www.wickedunlock.com/apple-iphone-3g/rs11wp9/ by providing informations like Country ,Current network name and IMEI number of the iPhone 3G .