Chronic diahorrea

My daughter is 4, from 10 months old she would often get vomiting and diahorrea alot, always low in iron, iron deficiency anemia. Was put down to lactose but I generally don't believe this is the case now. We tested negative for coeliac disease on stools but I think the dietician was unhappy that only one set of bloods for coeliac was done and not the second that she required to pin it down. Over covid my daughter managed well, she was able to tolerate the same foods as her brother even chocolate, she never complains about a sore tummy and was rarely sick at all, I always kept her on soya milk and dairy free cheese. But she would often have frubes and the odd chocolate biscuit or bar.

In the last 10 months she has had 10 episodes, she slipped thru the cracks as her consultant left, I'm off work alot with her, but each time I send a stool off it comes back negative for a bug.

It's like her body isn't processing the food, so the soya comes out or the dairy free yoghurt that colour and either mucous or complete diahorrea, I let her have oreos and then it comes out that colour of doahorrea.

And when she has vomit episode it could be 12 hrs after a meal, at like 2 am 3 am 5 am in the morning and the food is just regurgitated and not at all digested. Meat etc.

Even when she was on iron I felt like it did her no good it just came away. Have an appointment now but I think if they say milk allergy I'm gona be annoyed, cos that would show within 30 mins to 2 hours after ingesting. And would settle with tweekingbher diet.

Any suggestions why her food is either not digesting or completely running out of her.

Thanks