Reddit, Help! My friend refuses to give herself or her child a flu shot because she insists no evidence supports its effectiveness. Prove her (or me) wrong!

She says there's no scientific evidence supporting its effectiveness for her or society in general. She insists that the government/CDC is not to be trusted in spite of the fact that they recommend the shot for anyone over 6 months of age. She's gone as far as finding videos of doctors on youtube that support her claims in an effort to prove me wrong. I need an irrefutable, long-term study with evidence - does it exist?!