Should I go to the beach with my "friends" or not?

I think that you should go but you shouldn't worry about what Sara thinks about you. Don't let her ruin your good time just by saying those things! Now you know who your friends are and try your best to distance yourself from her because you know that at any given time she can go off! Just have a great time and act if she wasn't even there but be polite because you are going in her car and she is your transportation to and from the beach! Have fun!