Susan, the letter is about women in Bayonne and in the départements of France adjacent to Spain. The army was, however, not in those locations. Hence we are not talking about camp followers. Indeed, there was an entire civil administration that required evacuation.

I am sure there were camp followers among these people, but the letter is clearly not reflecting Napoléon holding the view that the French army was a mobile brothel, the spin you gave in when you quoted the letter.
"As for the mobile brothel, whatever the exact phrasing, it appears to have been a fair description, to judge by Napoleon's reaction:"

You can think anything you like of the letter, of course. But I would not expect anyone who can read French to agree with the spin you gave to the slanted English (mis-)translation.