You make some good points there! I agree with you that Darlie did it, but just to play devils advocate, there is in fairness a good amount of evidence countering these points.
1. The fibers found on the knife were only compounds that could have been made out of the same materials as some window screens. There was nothing to say that it couldn't have come from somewhere else, and it was never tied to the specific screen in the Routier home. When the knife was tested as well, few precautions were taken, and even investigators admitted that they didn't clean the surface in between testings, so after testing the screen, it is likely that there could have been transfer onto the knife.
2. Although there are stark differences in the way the boys were murdered and Darlie was "attacked" (and I use the word attacked with caution,) her neck wound was by no stretch superficial. The knife came two milometers away from slicing her artery, which would have killed her. In fact, the only thing that stopped this from occurring was a gold necklace that had to be surgically removed. There was also such a bad bruise going all the way up her arm, I have no idea how she would self inflict it. (I have attached some pictures below.)
3. In police interviews she said that she used the vacuum as a crutch, which makes sense since she lost a great deal of blood. She would have felt faint.
I actually never heard about the nightgown. Could you send me an article please? (Not trying to be condescending, I'm genuinely interested.)
In fairness though, the silly string was weird. I know supposedly before the party there was a graveside service with crying, but the silly string I just don't have an explanation before. It was weird.