Good for you to recognize that you can break that cycle!

Pick your battles. For things that are very important, sit down with her and make a chart together about rewards and punishments... when you discuss the whys and hows behind your desires for her improved behavior, and allow her to help make the decisions for when she does good and otherwise, then YOU won't be the "ogre" and won't have to take it personally when she makes mistakes.

Make sure you have the basic behaviors you want... whether it's eating all on her plate (don't give her so much?) or picking up her bedroom or doing a chore..
have the activity and then a column for reward and one for result if not done or improper behavior (like backtalking.)

Then when these rules are posted, you only have to refer to them, remind her she agreed, and enact it. You won't have to remind her of a reward for going the whole day without using a bad word... but you will have to remind her of the agreed-to timeout or loss of a privilege (tv, computer) if she messes up.

Doing this will also teach her how to self discipline and make plans and goals ... and will make the rule chart the punisher while you can still be the rewarder! It will help her learn to feel good about herself, that she isn't "only, always" a "screwup" as you phrased it. (and you aren't always one either mom!) See if she can help you help her..cooperate to make life easier.

Be sure to add in the love..tell her you love her..you don't always like how she acts, but that doesn't change that you love her. Surprise her with rewards "for no real reason"... so it isn't all about goals and punishment for not being "good enough".

Good wishes.