I am all for good manners and saying hello, etc. But it's 7 in the morning for heaven's sake! I am sure it was pretty obvious that your daughter had just rolled out of bed and was wiping sleep out of her eyes.
I come to the door and greet the children. Because that is MY job. My children live here, and they do thier part to be good to the dc kids. But I am not hounding them first thing in the morning, just to make one person feel "special". Did Mom tell her 2 y/o to say good morning to your daughter? Doesn't sound like it. And she didn't even bother to set a good example herself.
I would have just reminded Mom that she wasn't even awake yet.