Personally I wouldn't bother testing for celiac. I 100% believe your daughter is sensitive to gluten but she may or may not test as celiac so there's no point testing in my opinion. I second getting your family onto GAPS. Not only will you heal her SPD but you will improve the health outcomes in all areas for your whole family. Your daughter's SPD is just one manifestation of your entire family's health issues. GAPS is a grain free diet, so it is gluten free but more than that.

All the best. How are you all coping with the news? Are you getting good support for dealing with her SPD? OT is awesome.
Thanks for this! Trying to get my head around her SPD, it's all very overwhelming. I bought all these books to read to understand it better but am currently suffering anxiety so everytime i go to read the books I start crying/freaking out. She loves her OT and is so tired afterwards as its also a swimming day so goes to bed early which is never a bad thing haha. I have noticed a difference in her confidence with new things like she went down a water slide all by herself (we caught her at the end) which is something she would never do before.

I guess the big thing is trying to figure out what is 3yr tantrums and what is SPD? I get the feeling a lot of the issues we have been having is SPD related.

Keep on swimming!