I created a user for my wife on my MacBook Pro. All went smoothly, except:
Her name doesn’t appear in the menubar to show the drop down to switch users. My name appears when I’m logged in. Therefore, to switch users from her account, I/we have to log her out.
Internet access via wifi is slow to nonexistent on her account.
Can’t think why her account should have worse WiFi. Did you create an Admin, Standard or Sharing Only account for her? Does she have a different Network Location from you?