I've never been to see a psychiatrist or psychologist but autism is certainly very hard to detect in me. Usually they say that girls are very good at mimicking and therefore they don't stand out as much, this is true of me at least. Also girls generally get less attention than boys in my opinion, especially if they're well-behaved.
As a child I survived by a policy of extreme psychological self-denial, as an adult I survive by a policy of extreme material and social self-denial. I don't think I can keep it up for much longer though.