What's the best way to back up a Win 8 Pro partition ? (not usually a Windows user) [View all]

I ordered a used SSD drive and it came with a mint copy of Win 8 Pro for an HP laptop installed. I don't have a copy of Win 8 or Win 10 -- don't use anything after Win XP -- but my mom uses Win XP on her computer and I am about to upgrade her to Win 7 (purchased installer disk). Of course, it seems only prudent to hang on to this copy of Win 8, even if I don't have the installer disk or key because -- well, you never know.

Problem is, I don't have much (lim(_much-->none much) experience in backing up Windows partitions. I don't want to use the backup/restore within windows, because it doesn't seem to back up the whole system (correct me if I'm wrong, but when I tried to transfer the contents of Mom's HD to a Win 7 hard drive, there was all kinds of stuff missing. Next time I'm planning to clone her whole hard drive, then upgrade that to Win 7 with the installer.)

What's the best tool for putting this partition "on ice" until such time as I might actually need it ? Partition Wizard ? Gparted ? Some other Linux tool ? I tried copying a Windows 10 partition with Gparted and it wouldn't boot properly -- tried to repair itself but couldn't. I don't have a lot of empty disks sitting around to experiment -- in fact HD's are failing faster than I can replace them with SSDs -- so I need to remove this Win 8 elsewhere and partition the SSD for OSX and Linux. In principle I could leave the Win 8 partition in place and use Boot Camp but I'm not expecting that to be trouble-free exactly. So -- Win 8 has to be stored somewhere, in completely recoverable fashion. Any suggestions ? I'm trying to do this without going out and buying any new disks, because $$$ are *very* tight, and needed for several other higher-priority items.