I'm part of a private diagnostic team. We assess people of all ages, stages and gender - however by default we seem to have become rather specialised in assessing girls.
On reflection, lots of these girls have either been given a 'no' diagnosis by CAMHS (often because they didn't meet criteria on ADOS - or sometimes because they DID meet criteria but somebody on the team conducted a school visit and watched from afar then concluded that they had appropriate friendships).
Also, they often don't get as far as going onto the ASD pathway because they don't get past the screening stage. Lots of girls on the spectrum present with very subtle traits - for example 'socially acceptable' obsessions that don't stand out as unusual unless you consider the degree of the obsession rather then the subject of the obsession.
I agree with other posters saying that perhaps your DD doesn't have autism because she may have standalone anxiety (or other issues). But I have to say when I read your post, I thought she had lots of red flags - judging by my own experience of diagnosing girls.
She may well have been given a 'no diagnosis' twice - but unless she's been seen by a team specialising in picking up girls, I'd be dubious. Sometimes one team will have taken into consideration the views of the other team, too - when I review paperwork as part of referral, I often see opinions biased by previous assessment and a seed of doubt sown about the parents which seems to influence subsequent assessors.
I also agree that referral to the Lorna Wing would be helpful because they will use the DISCO assessment. I trained at Lorna Wing and we find this assessment most helpful in diagnosing girls.
To the best of my knowledge, the Elizabeth Newson Centre specialises in PDA (and lots of girls have this on the spectrum) but they are 'full' and not accepting referrals at the moment.
Good luck with getting to the bottom of it - it's incredibly frustrating and worrying a process to be going through.