Lemuroid is a great open source emulator. Vimm’s Lair is a great place to find games/ROMs. It’s difficult to play games though that require the bumper buttons on a touch screen. Maybe consider getting her a retro gaming handheld device. They can either run based on Linux, so an emulator, or Android which can operate like normal and then you can select an emulator to play. ETA Prime has lots of reviews of these devices.