Marie Anne Lenormand was a real and formidable person. Her connection to the deck sold under her name is essentially posthumous marketing.
What is documented
Marie Anne Adelaide Lenormand (1772-1843) came from Alencon and built a career in Paris as a cartomancer and fortune-teller across the Revolution, the Directory, the Empire and the Restoration, a period in which being publicly associated with prediction was intermittently dangerous.
She was known as the Sibyl of the Faubourg Saint-Germain. She was arrested and imprisoned more than once. She published extensively, largely memoirs and prophetic works trading on her connections. She made a great deal of money and died wealthy.
What is claimed
That she read for Josephine de Beauharnais, for Robespierre, Marat and Saint-Just, and that she foretold the rise and fall of Napoleon.
Some contact with Josephine's circle is plausible. Most of the rest rests on her own accounts, published by her, in books whose purpose was to advertise her practice. She was an effective self-promoter in a market that rewarded it, and her memoirs should be read as what they are.
What she did not do
There is no evidence she ever used this deck. The thirty-six-card system she is named for was in existence during her lifetime as Hechtel's game, but nothing connects her to it.
Her name was attached to a thirty-six-card cartomantic deck published in Germany by 1846, three years after her death. She had no part in it, took no money from it, and could not have objected.
Why this matters for reading the cards
Because it settles what kind of authority the deck carries. The meanings are not the recovered technique of a celebrated eighteenth-century seeress. They are a nineteenth-century German cartomantic tradition that borrowed a famous French name to sell itself, and that has since been developed by generations of readers who did the actual work.
That is a perfectly respectable pedigree. It is just not the one on the box.