I think she's trying to protect you. If your friends don't believe you they might think you are weird and not want to hang out with you. If they really are brainwashed I'm not sure how effective it will be to just talk to them.

I mean for example when I see the sky I know for a fact it's blue but what if it's really purple and I was just brainwashed along with the rest of the world into thinking it's blue. If you told me it was really purple I would think it was some sort of joke but if you persisted I might think you were the one who had been brain washed and stay away from you. I mean if we're all brainwashed then the majority of people would think the sky was blue so everyone I asked but you would say the sky was blue so that would be my proof and you would have none.

Maybe you can think of an alternate strategy like gathering more information on what people do believe and see if there are any difference from what you think?