My Almost 3 Year Old Has Always Had Floating Stools.

My almost 3 year old has always had floating stools. She needs to go a few times a day and they are often loose. She loves milk and drinks around 250-400mls a day but always says her tummy hurts about 10 minutes after consuming it. Other than that she has an extremely healthy diet including many fruit and vegetables, wholegrain bread and pasta, brown rice and loves chicken, fish and red meat.
I am thinking she may be lactose intolerant?