You could take the highly inconvenient Unraid 2 gamers 1 CPU approach from this video:
Which will require you to buy 1 or 2 more GPU's, possibly some more RAM too.
Or you could put together a simple gaming PC which is probably a lot more convenient. A Ryzen APU, dual channel fast memory no dedicated GPU will work fine for it.
EDIT: by the way, it's 1 or 2 more GPU's because you need 1 GPU for your system, 1 for hers and 1 for the Unraid GUI. The latter could run on your iGPU if you have that. Keep in mind you will need a good PSU to run those GPU's on!