I would definitely tell her that she must call/text as coming unexpectedly throughs everyoneoff their routine which you have worked hard to establish and the kids expect it. Prime example, her daughter's reaction.
If she shows up early again without notification, I wouldn't answer the door. Often if the doorbell rings and/or the phone I don't answer if I'm busy with the children. To me it sends a message to the kids doorbel/phone is more important.