This happened to me at age 7 and I believe it was from a sexual trauma that I blocked out but then carried this "sudden and newfound guilt" about everything in my life which still affects me today at age 40- including blaming myself for things that are not my fault- shame. Just felt the absolute need to share this with you, for whatever it's worth
It sounds like she suffers from obsessive compulsive disorder,pure O. I was the same!
I also came across this while researching something else and had to stop and take a look...because this was absolutely me as a child, and I didn't realize anyone else dealt with that. For me, it was mainly OCD, manifesting in huge amounts of guilt over every thing, even when I had done nothing wrong. I would make my mom come into the my bedroom before sleeping and "confess" everything I could think of. Please take her to a therapist. My parents didn't know about OCD or how to handle it and I suffered for much longer than I could have. Also, try not to get irritated and shut her down, it just makes it worse because there is absolutely nothing she can do to stop it herself. I'm also now a normal (ok, semi-normal ;)) productive member of society so it can definitely be overcome with the right guidance and therapy.
I had a similar experience when I was in Elementary school. This may not be the case with your daughter, but mine was a result of being bullied. A group of girls would point out everything I did or said wrong. If I held my fork the wrong way or said a fact that they thought was wrong, they would blatently point it out and say I was stupid for not knowing better and that's why no one wanted to be friends with me. In secomd grade, a couple of girls called me 'the girl who couldn't do anything right'. I became so self-conscious and guilty, the only way I felt I could absolve myself of my guilt was confessing every little thing I did. Things like talking in the hallway or eating my dessert before my meal. Once I even confessed to writing my name in all capital letters Kind of like with your daughter. This behavior went away shortly after the bullying issue was resolved. Maybe this isn't the case here, but I didn't tell my parents because I thought I was guilty and was afraid of getting in trouble. They finally found out when an aide witnessed it on the playground and told my teacher who called my parents. This may be something you would want to look into. Best of luck!
Ah, not sure if this is completely relevant, but that truly reminds me of myself.
Parents weren't around much so I was basically raised by my sister, I would cry over everything and confessed that I've done wrong until no one was willing to listen anymore.
Don't shut her out. That's the first thing you need to do. Shutting her out will likely cause the start of a pattern, inwhich she bottles everything up, which can cause a lot of trouble in her future.
I'd suggest therapy, personally. Look at her interests and see what therapy would fit her.
At the top of my head I can count atheletic therapy, therapy by music, and therapy by horseback riding - all are fit for children.
I'd also suggest getting a doctor to see if they can diagnose ADHD, ADD or any other disorder that may cause hypersensitivity, as a starter.
And, if it turns out that she has it? Support her, the whole way. Make sure she's confident that she can do the right things, even if they are hard, that she can get where she wants, through hard work.
Make sure you understand her if you want to understand her behavior.
I would second all of the advice to get her to talk to someone if this is an ongoing issue. She could just be a sensitive child, but sometimes it's an early warning sign for other things. I had the same constant need to confess things to my parents and so did my younger brother. I can't tell you exactly what your daughter is going through but for me the confessional urges came from feelings of doom, guilt and inadequacy. It felt like a generalized imposter syndrome. Later on in life both me and my brother were diagnosed with clinical depression and anxiety, which we believe is hereditary. The negative feelings and urges to confess went away once I got effective treatment. Not armchair diagnosing your daughter but it would be worth checking out.