Welcome Milly. Perfectionism is common in high functioning autistic females. Asperger Syndrome is no longer diagnosed, it is encompassed with ASD now.
If you are worrying how DD will manage to live independently I would think she meets the PIP criteria, although it isn't easy to get. Genuine question, what makes you think DD isn't eligible given your worries about independence? DD, or you on her behalf if you become her appointee, have nothing to lose by applying. Have a look at the benefits and work website and this guide.
Unless short term and working towards reintegration part time timetables are illegal whether or not parents agree. DD should have received medical needs tuition when at school and an EHCNA submitted. If DD still is attending full time or is struggling when there you should make an EHCNA request now.
Zoo speaks a lot of sense, you can't look after others if you don't look after yourself.
It's a shame you can't go Zoo. Next time you should go and give DD2 the option to join you or not. It's not fair on you or your other DC that you miss out. I think you've done the right thing with meals, 3 sittings isn't sustainable. The rest of you have needs too and DD2 can not continue to dominate you at the expense of yourself and others. You can't please everyone all the time, do what you think is right and ignore the fall out. With DS1 I find if you let it the MH condition takes and takes.
Much less stressful for all and safer with only one GA. DS1 has had a brilliant day. DH took the boys kayaking, previously the leader has given DS1 1:1 and they kindly did the same this time. He had also voluntarily been in the paddling pool, he didn't want to go in to the garden but once outside got in of his own accord.