E.N.
Well, my son is 5 and has been actin gas though he is three like his brother. While I was at my moms we started something new to help out. We seperated them by age. The 5 year old gets to do things the youngest does not while the youngest gets to do things the oldest can no longer do because he is not a baby any longer. When the oldest decided to act like a baby, we took away a big boy priveledge and put him in a corner or sent him to his room with the added phrase baby -(their name). It was not done in a mean manner and it worked within the day. You said you have a younger one and an older one. Try to do this with them. that way she will understand that she can not act like a baby and can not have her way. If she throws a fit in the store again, tell her that babies do not get anything from the store. Only good girls that act nice in the store and ask politely for things.