Actually..I think she was born illegitmate...but when they married..it legitmized her birth. The same thing happen when Stephanie married Daniel Drucet (her children were legitimized) and it would happen to Camile, if Stephanie married her father.
The following is from wikipedia (and yes, I recognize that some of the information from Wikipedia is inaccurate....but not this).
Born Charlotte Louvet in
Constantine, Algeria, she was the illegitimate daughter of
Marie Juliette Louvet, a cabaret singer, and Prince
Louis II. On the death of Prince Louis II, theretofore without a legitimate heir, the throne of Monaco was due to pass to the German
Duke of Urach, Louis II's cousin, a son of Princess Florestine of Monaco; to forestall this event, on
15 May 1911 a law was passed recognizing Charlotte as Louis's daughter, and making her a member of the sovereign family. Though it was later held to be invalid under the 1882 statutes, an Ordinance of
30 October 1918 allowed her to be adopted. Louis adopted Charlotte in Paris on
16 May 1919, bestowing on her the surname Grimaldi and the title
Duchess of Valentinois; she was thus his
heir apparent as Hereditary Princess from 1922 until
30 May 1944