My friend is in the middle of a custody case, and its getting pretty ugly! His daughter has been in the custody of her mother , the last 90 days! They live with her parents! Her parents are everyday marijuana users! He was just granted wed. and weekend visitation! He Had a hair follicle test done on his daughter , last week oct 13th 2015! How accurate will this test be?

If they are actually everyday users... and not just accused of it. It WILL show up on the test,

The hair follicle test is pretty accurate. How accurate will it be with second hand pot smoke? I am not completely sure. Chances are, if they're habitual users, she might test positive.

Not only are the tests accurate, they can differentiate a habitual user from incidental contact by detection levels, going back 90 days. Whatever lab your friend used can explain this more fully.