You see this attitude doesn't help anything and annoys me. The person sitting next to your daughter did nothing wrong. You had options and if you choose to not exercise those options to try and save a dollar that's on you. An eight year old should be able to behave and not spill her drink on someone for a few hours. I assume she does as much while at school. If not, again that's on you as a parent. You and your child are no more important than any other person on that plane.
If I was next to your child I would have my headphones or ear plugs in and either sleep or listen to my music and read my book. So her talking wouldn't bother me. As for spilling juice on me I would ask the flight attendant to find her parent and get your address so I can send you my dry cleaning bill.