Fedex will likely handle this for CAD 70 or so (could be a lot more if it is heavy or valuable). Bear in mind that if it has a lithium battery, you may need to toss it and that you will also likely need to provide a clear explanation of the fact that the laptop belongs to your niece and was not purchased in Canada on this trip. May need to translate that into Czech for easy reading on arrival. Finally, given security screenings, you should back up the hard drive before shipping and hang onto the backup on a flash drive or somesuch until the laptop arrives and your niece verifies that all is in order.