How did Sacagawea join the lewis and clark expedition?

BECAUSE SHE WAS A INDIAN AND had a CHILD AT THAT TIME AND SHE IS IN THE BOOK NO LIE JUST LOOK ITS RIGHT THEIR CHECK IN a book IT WILL SHOW YOU THE EXACT THING im talking about in a library at school ANTWHERE IT WILL BE THERE I WILL GIVE YOU A ONE YEAR GUARATEE YOU IT IS AND IF IT IS YOU OWE ME A APOLEGY AND U HAVE TO SYA sorry TO NO LIE TRY AND DONT CRY