Has Mary ever appeared to you while on a mountain, most likely the answer is no (or any other dead person for that matter). You would be one of the most jubilant people alive. You cannot dismiss that she did appear to Saint Louis de Montfort, because she appeared so many times.
You're sure it was Mary that appeared to him ? How would he know if it were really she or not ? How would you know if it were really she or not ?
Remeber, ... the Mormons say that God, the Father and Son appeared to Joseph Smith, too.
SD