My daughter is autistic, and my sister in law has a diagnosis of bi-polar effective disorder, however, after having been on countless courses and read many articles on autism presentation in women, I am convinced that she is also autistic.
Depending on your personal circumstances, I would suggest going private for a diagnosis. If you do, go to somewhere with experience of female presentation, such as the Lorna Wing centre if you are in the South.
It is very difficult to get a diagnosis for a child who is obviously struggling, and the waiting list is over 2 years. We ended up getting a private diagnosis for our daughter and the cost was c £1700. It's not cheap, and, to be honest, it doesn't bring much in the way of post diagnostic support.
I would maybe start by reading some of the many excellent books and articles written by autistic women. Odd Girl Out by Laura James is a very moving story of the author's journey to diagnosis,
The Girl with the Curly Hair has lots of resources, and is also running online seminars at present.
Try looking for Tony Attwood talks and Temple Grandin.
There are lots of women who have self-diagnosed their autism after trying and failing to get support/help from the NHS.
For many, reading about it was their lightbulb moment. I think (certainly for my daughter) the understanding that there was something different about how her brain worked, and that it wasn't her being weird has been transformative for her. The support she needs is around coping in school - anxiety is a massive issue for her, and with that comes coping strategies that are self-destructive - self harm and eating disorders.
You could also try finding a therapist with a speciality in female autism. Try BACP for reputable therapists near you.
90% of the help and advice I have had for my daughter has been via charities and support groupd on facebook. I have been passed from Step 2 to CAMHS to PALMS - we are lucky in that we can afford private art therapy for her, which has been massively beneficial for her.
I am not autistic myself, but it often runs in families, and I am fairly sure my husband is autistic. I think it's helped him to think about traits and understanding his own reactions to situations. He has no desire currently to seek a diagnosis, but I would support him if and when he decides this is important for him.
Good luck with some answers