If, as you mention, the "C" drive contains the OS and has a low capacity (50 GB, as you said), the easiest solution is to increase the "C" partition's capacity. Since the drive has such a large capacity, 500 GBs will be more than enough.
There are many utilities --some are freeware-- that can be used. A good one that comes to mind is 'PARAGON Partition Manager". I use version 12.
She may ask the friend who installed the 2TB drive to perform the task, that is, if he/she knows how to do it!!!