Without an IEP or 504, your reaction will need to be with velvet gloves rather than a wrecking ball. If you were going to be staying at the school, it would be worth pushing a lot harder to make sure there was a different understanding moving forward, but this would simply be the impetus for me to begin the process of getting her covered by an IEP or 504 for next year.
I think an email to her teacher and to the psychologist is warranted, just asking that in the future your daughter not be given writing assignments as punishment since writing anything at all is already punishment under the best circumstances. It will document the issue, your concern, and may help another child further down the road at that school.
As to whether your daughter did it or not, you'll never know for sure, so this is likely a good teaching moment for you with your daughter rather than a defending moment with the teacher - don't get pressured into confessing something you didn't do, but if you did do something being honest and taking responsibility will usually mean there are less consequences long term (loss of respect, trust, etc.
I've learned that kids I never thought would lie to me did indeed lie to me with great skill, and that the egg on one's face after valiantly defending a child who promised they weren't lying until infallible proof showed up is quite uncomfortable and destroys credibility with the teacher for the next time I needed to go to bat.
Hope this helps...
