It's normal for a baby to be gassy- doesn't necessarily mean that something is wrong. If it's not a big deal for her to cut out dairy then I can't see the problem with doing a trial. I found being dairy free while nursing to be extremely difficult. I was always hungry and lost tons of weight and there was so much that I wasn't allowed to eat.
Looking back I realized that DS1 had green unhealthy looking stools before the blood showed up. But he was my first and I didn't know the difference. It was only afterwards that I realized the screaming, gas, green stools and blood were all related. Many people cut out food groups from their diet unnecessarily for the sake of bf. It could be her doctor is coming from that viewpoint.