I don't think your mom friend did anything wrong. I think it is AMAZING that all the boys in the neighborhood have been so understanding about this little girl affecting how they play all this time. I know that MY son (who is now 12) would be very watchful and careful around a younger child as well, but not days on end. There would come a point, probably long before now, when he would have complained loudly that the little girl was in the way..... again.
It probably is hard on the girl's mom, though. Her child is so much younger and it is hard to be the ONLY MOM who cannot take 10 minutes to herself to chat with the neighbor friends while the kids play, b/c her child is constantly in danger. It is just a fact. Her child is younger and requires more close supervision. She is jealous (whether she knows it or not) that she can't "hang" with you guys. And I'm sure it is WAY easier for her to fuss at the older kids than to have to walk away from the adult conversation to retrieve her (now) tantrumming daughter. It is a hard and lonely place to be sometimes. But such is life. The sooner she learns to deal with it, the happier you ALL will be.
But, no, I think your friend did the appropriate thing. And I APPLAUD her.
Wanted to add:
the SMALLEST age gap is 4 years. That is WAY too big of a gap for this little girl to be trying to play with these boys. At age 2, she has NO CONCEPT of watching out for herself. It is totally inappropriate that ANYONE should be expecting the older kids to be playing with her. She might watch from the sidelines (doesn't sound like she is getting any guidance on how to do that though), but should NOT be out in the midst. She is just too young. Her mom needs to find some age appropriate playmates and schedule some play dates for her. Perhaps if she did so, she wouldn't be out in the middle of the boys' activities all the time.
If they moved from elsewhere (not just a different neighborhood, but different town), has anyone tried pointing the mom in the direction of a moms group nearby that might have like-aged kids that she could hook up with?