There are a handleful of seasonal recipes that have been removed from our Cook Books throughout the years, only to return for limited time runs and a few others that are only available through Special Editions of the game. As you might've guessed, the Love Muffin is one of these recipes.
This is one time when Android users have the advantage as they are able to access multiple versions of the game simultaneously while iOS users are stuck with one version at a time. It's likely your neighbor was a droid user, playing on an older Valentine edition of the game (despite it not being recommended) and that's how they were able to retain access to this recipe.