It is very hard if she is never there to assist ( let it be small problem, let it be national crisis, she is never there ). and the only moment she take action, she get her flank kicked ( only for it to follow with Celestia refusing for Luna to go to crystal empire and help, while telling Twilight "in the end it must be you and you alone" ), yea, not the best impression.



Another problem is that even if we got flashback where Celestia took action against Nightmare Moon and Discord, it is followed with her and Luna being very easy captured ( Princess Peach stereotype ).



So yea, the show do not leave Celestia with good impression, and even the flashback does not save her good name if she is forcefully removed from action every single time.