I'm not sure what a 'stage 2' meeting is, but I met with an EP as part of my DS's EHCP assessment process.
I had a two-hour meeting with her and she was lovely. She really listened to all my concerns/observations about DS and definitely had my Ds's best interests at heart.
I spent some time writing a list of all the things I wanted to cover off before the meeting as it's easy to forget things. She asked a lot of questions about Ds's history so again it's helpful to make a timeline of things - eg when they spoke, dates of any diagnosis, examples of difficulties they have in class.
The meeting is your opportunity to advocate for your DD and to really spell out the difficulties and barriers to learning you feel she has. If it's appropriate, you can also mention things like struggles to make friends, if it's hard for her to access clubs/hobbies/relationship with siblings etc.
She also asked me about what sort of school setting I thought would suit Ds best. I'm guessing at 15, the EP may talk about where you and DD are thinking for post 16 - and probably exam allowances?
She then observed DS in class and spoke to his class teacher/support worker. She also took Ds out of class to speak to him and he did some sort of cognitive tests.
After she wrote the report, I then met with her again to discuss the report and I had the opportunity to amend anything that wasn't factually correct before it went off to the local authority.