saffron

hey guys...hows it goin? i'm ok...4 exams this week and a li'l bit of drama. tell me how i should handle this...
my best friend and her boyfriend are really close with me and my boyfriend. we're a cute li'l group, and have a lot of fun together. (maybe too much sometimes...) anyway, they used to smoke up with us, but stopped about a year ago due to her boyfriend's job as a welder. (much to his dismay, he's such a pothead.) the other day he got a new job and took his one and only drug test and passed, of course. this weekend he came down to work on my boyfriend's car with him. we were talking about smoking, and suggested it to him. he begged me not to tell his girlfriend, my best friend, and i agreed, cuz he is a big boy and was planning on getting her to smoke sometime soon. (she's not that big of a pothead, but she enjoys a nice smoke every now and then.)
so i didn't tell her. because i'm quite close to him too. turns out he tells her, and she is super upset with me for "pushing him into it" and keeping it from her. i do feel bad, because she's my best girl, but i don't feel like i should take all the blame for this. what should i do to gain her trust back/ make her feel better??