Hi,
Firstly autism is not a mental health condition so you'd be much better reporting your post and asking MNHQ to move your post to
SNChildren www.mumsnet.com/Talk/special_needs
or SNChat www.mumsnet.com/Talk/special_needs_chat
where there are loads of posters who can advise you as their kids have autism and they've been through the diagnostic process.
Q1 - It's not just answering questions, it's very specific questions and observed responses done in a clinical setting by professionals. For a diagnosis, impairment in three specific areas has to be present from childhood. Google Triad of Impairments
Q2 - A person with autism responds very differently to things as their brains are actually wired differently to people without autism, usually referred to as NT, short for NeuroTypical.
The two are not really comparable in some of the same situations.
Q3 - Only to a certain extent. Google Executive Function.
Q4 - No, intelligence is not a diagnostic factor in autism. Autism can affect a whole range of people from very very intelligent through to not very intelligent.
Q5 - no again, there's much more to autism diagnosis than milestones although knowing when they were reached or not can be helpful.
Do research and read up on Autism www.autism.org.uk/ and the diagnostic process but do be aware that autism can present very differently in girls and women.
Do research and read up on conditions that are co-morbid with autism. e.g sensory behaviours www.falkirk.gov.uk/services/social-care/disabilities/docs/young-people/Making%20Sense%20of%20Sensory%20Behaviour.pdf?v=201507131117
No-one's bashing you but to be the most help and support for your daughter, you also need to fully understand her condition and how she presents. You need to identify her triggers and learn to reduce the impact of certain things she reacts to, find interventions to help her. You also need to be able to advocate for her when she needs you to.
You have a steep learning curve ahead, good luck!