Two allergy doctors that my family has used and highly recommends are Howard Lang (far north Bedford) ###-###-#### and C.R. Hamel (south Arlington)###-###-####. We switched to Dr. Hamel after moving to Mansfield.
Both doctors spend a lot of time with their patients and dig for answers. Both doctors uncovered problems with family members that other doctors had blown off or passed off as a different problem than they really were. They will LISTEN to you and value your input into your own (and your child's) medical care.
Before going to an allergy doctor, be sure to ask a few questions on the phone. There are two doctors recommended in the other responses who don't believe in food allergies and who won't let you do injections at home. With an infant, you'll probably want to take the precaution of doing it in the office anyway (if anyone will treat an infant with injections--I don't know), but she will grow older and you will get tired of spending time with appointments to get injections twice a week. We have five people in our household who take injections at home. We've NEVER had a problem other than once I got a headache from a dose that was off.
Be alert for other things she may be allergic to, because most allergic people are allergic to more than one thing. Ragweed and grasses are likely allergens for her, because they cross-react with milk.