Simplify the following text for a Grade 9 native English-speaking person.
Original: Louise Henriette de Bourbon ( 20 June 1726 â `` 9 February 1759 ) , Mademoiselle de Conti at birth , was a French princess , who , by marriage , became Duchess of Chartres ( 1743 â `` 1752 ) , then Duchess of OrlÃ ans ( 1752 â `` 1759 ) upon the death of her father-in-law .
Simplified: Louise Henriette de Bourbon ( 20 June 1726 â `` 9 February 1759 ) was Duchess of OrlÃ ans and the mother of Philippe Ã galitÃ .