Rude sister in-law

I really do like my boyfriend's sister. But she is kind of a difficult person and sometimes it just exhausts me to even be in the same room with her. Today she just drove me nuts. I finally got into the university of my dreams and am going to be a teacher (hopefully). Her comment to that: " didn't you like study already? You will still be studying at age 40!" (I'm 22 btw)... So I said 'well I'm going to be a teacher... It's ok." Her answer was "well teachers are cowshitters anyways.."

I was really hurt and she made fun of it.

How can I get along with that. I'm really sad about it.