Simplify the following text for a Grade 7 native English-speaking person.
Original: Only some personal and family letters remain ( by one estimate only 160 out of Austen 's 3,000 letters are extant ) , and her sister Cassandra ( to whom most of the letters were originally addressed ) burned `` the greater part '' of the ones she kept and censored those she did not destroy .
Simplified: Only a few letters remain ( it is estimated that only 160 out of Austen 's 3,000 letters survive ) . Her sister Cassandra ( to whom most of the letters were written ) burned `` the greater part '' of the ones she kept .