Norton 360 3PCs

I've installed this product onto my computer successfully - is it possible for my daughter (in London) to use one of the 'seats' - my account says there are two available and she has tried to install one using my product key but gets the message 'the product key you entered is either invalid or it has been used with another account'.  It has been used, with my account!  Any ideas?  Does it only work if I have 3 PCs, at home, with me?  Thanks

You are correct, Norton Family can be used on any device, even those that do not have Norton Security or Norton 360 installed.