First, you will not have to deactivate Windows 7. If you do install it on another computer, it will require a call to an automated system that will use the numbers generated by your system and give you numbers back to use to activate. There should be a place during the process that will direct you to the correct utility.
Windows 8 will normally come with a system set up for Secure Boot. This means a Windows 7 DVD will boot, but not be allowed to install. For it to work, you would have to change the the Compatibility Support Module (CSM) settings. You would normally need to Enable the CSM, but how this is actually done depends on your specific system.
But might I suggest, in about a month, the Windows 8.1 update is going to be released to the public. It makes some changes which allow her to boot straight to the Desktop and maybe some others settings that will help her out. But it does take some getting used to, so perhaps wait until after that update to make a decision. I do not use Windows 8 as my primary system because I do not like the User Interface, so I understand her situation. While you are thinking about it, you might jump over to the Windows 8 forums and ask any specific Windows 8 questions there. Perhaps they could give you alternatives to the problems she is experiencing.
You can make an Image backup of your system if you want to try. I do not have an OEM system so I have not made an image of one of those and do not know if it will work or not.
How large of a Flash Drive does the Recovery Drive utility say you will need for your system?