How to transfer iTunes library between user accounts on Windows?
Under the old user, launch iTunes, then Preferences, then the Advanced tab and discover the "iTunes Media folder location".

Switch to the new user and launch iTunes. From the advanced tab, verify that the new user location path corresponds to the new user name. If it doesn't, quit iTunes, create the iTunes Music folder (using the path structure of the old location as a guide).

Relaunch iTunes. Set the location to the new folder you just created.

Quit iTunes and use Windows Explorer to copy everything in from the old user folder to the new user folder. Launch iTunes from the new user and your music should be there.