The question is what causes your child's symptoms. Does she get stomach aches and diarrhea after drinking milk or eating dairy products? If so, she might be lactose intolerant or have milk protein allergy. If her gastrointestinal symptoms don't seem to be related to dairy products, she might have some other food intolerances or allergies. Schedule an appointment with your daughter's health care provider for an evaluation of her symptoms.
Probiotics are bacteria or yeast products that are used to try to repopulate the human digestive tract with organisms that hopefully promote a healthier digestive system. Examples include Lactobacillus acidophilus (in yogurts), Lactobacillus GG, and yeast including Saccharomyces boulardii.
Probiotics might help decrease the risk for antibiotic associated diarrhea and possibly some infections. However studies do not show a significant impact of probiotics in preventing diarrhea that occurs in most children. Probiotics may have other benefits that are still undergoing investigation, including preventing or decreasing risk for allergies in young children, treating irritable bowel syndrome in older individuals, and even preventing cancer. The risk of taking probiotics appears minimal, so many individuals choose to use these for the potential benefit.
There are many forms of probiotics, most available in capsules, powders, or contained within foods. One problem is that the control of the content of these substances is often lax, so reliable counts of bacteria in each capsule or comparing one product to another can be problematic. The FDA does not regulate probiotic products.
If you choose to give your child a probiotic, discuss this with the pediatrician to make sure the product will not interfere with any other treatment(s) your child may be taking.
Below is a link to the NIH website with more details about probiotics.