Did she get too busy and forgot because of running around, or did she just not care. That is two seperate things. If it was a honest miscommunication and your daughter never reminded her, then I would not make a deal out of it. If she just don't plan care that is different. Many people including myself expect kids about that age to start thinking about their own care. I will still make lunch for my son, IF he asks. He is 12 now, but I probably started not reminding him to eat every day about the age of you daughter. Not all the time, but sometimes, I was busy and he could make a sandwhich.
I do not know your history with your mom so I do not know what to say really. If it had been my mom or grandma I would not be upset in the least, but I know they would never intentionally not feed my son, of course they love food, so I know it would be true oopsy becaue they forget to feed themselves.