Boona - be careful. To you, your daughter is everything, but she is 10 years old and the story that she has given you is not accurate. There is too much wrong with it. There may be something in parts of the story but she has definitely exaggerated the circumstances to suit herself. She has definitely played down her part amd played up the other boy's part.
It sounds like the school did get to the bottom of the situation, but the result is not what you wanted to hear. It sounds like they blame your daughter entirely. I wonder why that is, if indeed the boy was a known bully.
I suspect that they are treating your daughters cut lip as an accident when he flung his hands backwards to try and catch hold of something to stop him going down the slide.
Therefore by all means ask the school for their version of the events but don't expect it to be the same as the one given by your daughter.