Think you are just going to have to do your best to keep your patience and continue with what you are doing - have her sit the whole time if that is your expectation and ignore the "all done's". It is typical, though annoying, for kids that age to repetitively say the same things over and over.

Both my daughters find it a challenge to sit still while eating, it is an ongoing battle. Some kids sit nice the whole time, others do not.