What encouraged Mary to leave the reservation?I know that Junior was an inspiration to Mary (because he was brave enough to leave the reservation)...

I think that one of the motivations for Mary leaving the
reservation was the grasp of the inward pull that it has on those who stay.  Although
Mary was extremely talented and very skilled in what she thinks and believes, someone
capable of greatness, Mary stays in the basement and can understand or feel her life
slipping from her.  Certainly, seeing Junior trying to achieve his own dreams outside of
the reservation is one element that compels her to consider leaving herself.  She
finding someone with whom she can escape also is a motivation of her departure from "the
rez."  The notion of being able to escape and live out her own sense of identity is one
compelling element.  Yet, to be able to do this with another becomes the force that
galvanizes her into action.  Junior understands this as his sister "trying to live out
her dream."  This involves being able to be far away from the inward pull of the
reservation.  Mary recognizes that if she does not act on her freedom now, she will
become like her mother and father, beings who are trapped by what is and have
extinguished any hope of what can be through alcohol and a mind- numbing existence.  It
is in this realization that Mary leaves.