ok, am on phone, so can't link, sorry.
the diet dd1 follows is a gf/cf (gluten and casein free) diet. it is researched by a unit which used to be at Sunderland uni, but have moved now and I can't rememebr their new name - if you google Sunderland ARU you should get re-directed.
There is quite a lot of info on the Sunderland protocol - you could try asking over on SN too, as a number of us over there follow special diets.
books wise, there are a couple by Marilyn Le Breton which are worth a read. Both also contain useful recipes on how to get around cooking without some usual staples, so are handy in that respect too.
Natasha Campbell-MacBride also has a good book out. She recommends the SCD diet, which is quite extreme. But again, reading up about it might ring some bells.
I don't now how much you owuld want to go into this yourself. as dd1 is AD, bowel issues don't get investigated, and so I have had to research it all myself. So I can't judge (and it isn't my place ot do so anyway!) whether the tests you are waiting for will be worth it or not. my only experience of doctors is them telling me that dd1's bowel issues are to be expected, and that thee is nothing that can be done for her.
when I then returned, having found out this info re: special diets , they dismissed it as not valid, and cautioned me against using them and trying ot manage it myself.
But I have seen so much improvement in dd1's that is has all been worth it.
If I were you I'd have a read around and see if you can dig up info on your dd's symptoms. It is horrible to see someone you cae for in so much discomfort.
websites which support ASD parents/children often have info on special diets, and very informed people on them, and also vaccine damage support websites. Again, I mean nothing by suggesting htis, just trying to give you some pointers as to where to find people who might understand what you ae going through 