Just wanted to come back to thank those who responded and an update if anyone ever searches this.
DD ended up in hospital with dehydration after my post which was not unexpected. It was much easier to get her seen and dealt with without a struggle this time, I guess we’ve reached enough admissions/GP appointments that they believe us when we say she’s going downhill now.
For the first time, despite asking in the past, we were offered an antiemetic. Which unfortunately didn’t work. We were admitted and she had three bags of IV fluids and as has has happened previously, once the cannula was in and she was receiving the fluid, the vomiting stopped and she began to recover.
I had a good chat with the consultant, who ruled out cyclical vomiting syndrome as suggested by a PP (thank you though for your suggestion, the thread you mentioned made interesting reading). It was ruled out as we know a trigger for every vomiting episode (virus, tummy bug etc) which is unlike CVS, where the vomiting seems to come from nowhere every three to four months.
He suggested that DD gets depleted very quickly (she is very skinny at the best of times despite efforts to build he up) and that she works into her limited reserves which makes her feel sick and it becomes a vicious cycle. He advised that, after a vomiting episode, we should try to get her to drink sugary drinks like fresh fruit juice, full sugar squash or lucozade to boost her glucose straight away (we already do try to do this pretty soon after a vomit but not immediately). We should also try to encourage her to eat as soon as possible, which is definitely something I don’t do if she doesn’t want to, which she never does. He suggested giving her as starchy food as she will tolerate. On top of this, he said he was going to add to her notes that the GP should prescribe a different antiemetic to be administered ASAP when a vomiting episode starts.
Unfortunately, having got home from hospital on Thursday, DD had a backwards step on Saturday and started vomiting again, despite managing to eat as recommended pretty well and drink as recommended very well. So we got onto 111 and managed to get the new suggested antiemetic, which worked. We also encouraged more of the recommended eating and drinking (cooked cold pasta pieces went down well, as did fizzy lucozade with the fizz removed and fresh apple juice).
I hope this helps anyone who might be desperately searching for ideas when their DC are continually vomiting. It is nice to have a bit of a plan now.
Thanks again to those who replied to my OP.