Personally, I would have her checked for any health issues/imbalances related to aging. Dogs can suffer from dementia and all, too. She might actually BE "losing it," as you put it.
If that's the case, you might be able to put her on medication that will help, or you might have no other choice than to either put her down or keep her separated from the other dogs.
If that's the case, you might be able to put her on medication that will help, or you might have no other choice than to either put her down or keep her separated from the other dogs.