If you haven’t created an account for your wife’s laptop, then the email would be unrelated to that as avast doesn’t send emails to you but would use the UI to notify you of impending re-registration requirement. First pop-up notification around 60 days, then 30 days, then more frequently.

The avast account appears to send an email to the email address for that account at 30 days.

You don’t physically have to have an account linked to your installation so it should work as normal as far as re-registration goes, but as I said there is nothing to stop you linking her installation to your avast account.