Good day pratchbatchpratch! I am Independent Advisor Paul R. and also a Microsoft/Windows user like you and I am glad to be able to provide assistance to you today. I understand that you are looking into installing Minecraft Java Edition on your daughters PC. As it looks like that you have already redeemed the code, you can instead login your son's account in Microsoft Store (if it is where you have redeemed the game) and download/install the game to the other PC as the code will not be transferrable and it cannot be redeemed twice as well.
You can also check out the link below with regards to switching from demo to the full version of the game.
https://help.minecraft.net/hc/en-us/articles/36...
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Note: This is a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.
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Regards,
Paul R.