Advice about 14 year old daughter I suspect has autism

Hi all, I've never posted in here before and I'm really hoping someone can give me a bit of advice.

I already have a son (11) who has asd and had been diagnosed since he was 4.  With my daughter the situation is a bit different as it's only recently that I've suspected that she also is on the spectrum.  She has a lot of traits that have become more and more apparent in the last year or so and this has kind of blindsided me. 

My question really is where do I go next. She obviously will need to be assessed but is this something a gp will refer for or does it need to go through her senco at school? It was a lot different with my son as it was the health visitor that referred him

If anyone could shed any light I'd be really grateful.

Thank you  x