If your main concern is keeping the child from developing depression and anxiety, it is good to realize that autism doesn't cause either, rather situations arising from misunderstanding.
Don't assume the child is doing something to be a jerk, communicate (And I mean listen to what the child has to say), accept the child as s/he is, work with her/him to handle any issues that come up, embrace his strengths, give him/her breathing room, realize that people on the spectrum especially are known for absorbing others moods without realizing it so keep yourself in good health, teach him to handle bullying and perhaps help him find friends that won't chastise him.
This goes even if he/she isn't autistic.
The previous advice by others is basically what I would of said, for diagnosis though I feel that childhood aspie test would miss a lot of young girls.
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Diagnosed autistic level 2, ODD, anxiety, dyspraxic, essential tremors, depression (Doubted), CAPD, hyper mobility syndrome
Suspected; PTSD (Treated, as my counselor did notice), possible PCOS, PMDD, Learning disabilities (Sure of it, unknown what they are), possibly something wrong with immune system (Sick about as much as I'm not) Possible EDS- hyper mobility type (Will be getting tested, suggested by doctor) dysautonomia