Thinking my 11yo DD is intolerant to gluten and dairy

My DD is 11yo and has ongoing digestive issues which have been getting worse. I know on her bio-dad side (no contact for over 7 years) there is a long history. Bio dad is lactose intolerant and bio-gran is lactose, gluten, soy.
DD says her tummy hurts after too much milk, bread makes her gassy. She bloats like a balloon sometimes and her bowels are either one extreme or the other.
Should I have her tested before eliminating from her diet? Which is more likely to be the issue gluten or lactose?
My other DD is 16 (different dad) and has issues with too much dairy but as long as she is careful and doesn't pig out on ice cream is ok.

I recommend getting tested. With dairy, it could be lactose or casein or both.

gluten intolerance could be Celiac disease, which is a serious autoimmune disease. If it's celiac, it's important to have a correct diagnosis, as gluten doesn't just hurt the gut, it also causes irreparable damage to other organs. A diagnosis of celiac requires a biopsy of the intestines to see if the villi are damaged. For that, she still needs to be consuming gluten. If you stop gluten and the gut starts healing, a biopsy won't find anything. I stopped gluten before getting tested and so I can't get a correct diagnosis. This means I occasionally consume gluten and I don't know what kind of damage I'm doing to myself.

For the gluten intolerant, consumption can also affect brain activity, behaviour problems, moods, fatigue as well as other issues. I'm not familiar with problems from dairy. I've only just stopped dairy for DS3's sake.

i highly recommend getting a referral to an allergy doctor, although you may need to wait months to see one. A GP can refer to testing as well.

I second what L&B has said. My mum has coeliac disease and has serious health issues from the complications of the disease. Please please please get tested properly before eliminating anything from your diet.