Need some info quick to help my cousin keep bf! Elimination diet?

My cousin's 4 mo has been having digestion problems and his ped suggested that the baby might be lactose intolerant. The babies father is of Mediterranean descent, and lactose intolerance is fairly common among this ethnic background. My cousin has gotten the idea that she won't be able to continue breastfeeding. Couldn't she try an elimination diet first to see if he is just sensitive to dairy that she consumes? I don't know how to advise her. Please, link me to info about lactose intolerance and bf or elimination diet. She does not have Internet access so I need to print out info to mail to her.
Thanks so much, mamas.