Mint does not seem to do that
The user guide to Mint lives here: http://www.linuxmint.com/documentation.php
. It includes the installation steps, and those make it pretty clear it is not a drive-by process. There are quite a few checks and questions to be answered before it installs to the drive.
I would first get positive confirmation that there is not a DVD in the drive, and the any flash drives have been removed before rebooting the laptop and see what happens then. If not the flash drive, whoever hacked an activated Windows on that laptop may have used a Mint DVD to transfer the image and then left it behind.
If Linux is indeed installed on the laptop then things get a bit more complicated. The user guide will help you walk your friend through the steps to pull up the file manager (Nemo). See page 22 of the 17 edition. I would expect the Windows partitions to show up under the Devices branch in the left sidebar, although they may be labelled like "125 GB filesystem" rather than e.g. "Windows System".
Assuming the Windows partitions are still there*, the simplest way forward will be to get a dual boot going, then setting Windows as the default OS.
*I fear they're gone. Mint uses the Grub 2 boot loader and by default, it will add entries for other OSes to the boot menu. I would actually expect 2 entries for Win 7 as it will pick up the small Win 7 boot partition as well as the main system partition as separate installs.