What can I do to help her?

I have suspected ASD for all of my daughter's life. I've tried to get help/referral on many occasions but I've either vegb looked at like I was crazy or the odd doctor who did take me seriously referred but then we were rejected. So she's not diagnosed.

Anyway, fast forward. She's now 17 and agoraphobic. She's been home educated for 4 yrs. 2 of which were amazing and it was so obviously the right thing for her.  She was happy, more content, not one ounce of anger (when she was at school she had meltdowns most days), she made lots of friends and she felt good. Then anxiety hit again and she closed in. Constant panic attacks and crying and sleeping on my bedroom floor for 4 months (this exact thing happened to her at age 4, 7, 9 and 12 and this time she was 15. After 4 months it disappeared in that she was happy again and slept alone etc but it has left her with agoraphobia. She will come out with me which I'm trying to do most days but she won't go into buildings or where there are people. This has been going on for 2yrs now. She can't sit her exams or go to college (both of which she wants to do). What can I do to help her? She knows I suspect asd and I've suggested a private diagnosis but she won't agree. She's just waiting until she's "well" again so she can get on with her life. How can I help her to move forward without stressing her out more? All I want is for her to be happy.