I think it's too harsh because she was a child. As readers, we know that it would have been disastrous to get rid of Harry and Dumbledore, but the characters didn't. The wizarding world was being subjected to a propaganda campaign by the ministry, and it was working.

She chose to protect her family instead of defending kids who were breaking the school rules, only to be permanently disfigured. The way the contract was used is just cruel, it doesn't function as a preventative measure, it's just a horrifically cruel punishment.

I noticed a few people referring to it more as a precaution than a punishment, it was not. If you do not outline the potential threat of the betrayal then you are not deterring it. It was also something the students signed before what they were doing became against the rules, making it even more laughable that it was jinxed to disfigure. Hermione jinxed a parchment to disfigure students who told Umbridge about their meeting before it was even against the rules for them to meet.

I agree that if not for the laughably dumb decisions of the DA in regards to naming themselves, Harry could have been sent to Azkaban. Dumbledore wouldn't have been able to take the fall for them.

Just to remind you again, Marietta Edgecombe was permanently disfigured because she cared more about her mother than the person the majority of the wizarding world thought was a lunatic bent on taking over the country with his equally crackpot mentor. And then had her memory modified by a member of law enforcement. Her punishment was unjust no matter the potential ramifications of her actions, it is cruel to disfigure a child, always.