I like to imagine that Rainbow Dash sees Scootaloo sulking at the night sky one night without Scootaloo's knowing. Suddenly and out of nowhere she puts her wing around her. She must know what Scootaloo is thinking. She must also know how important flying is to her.
Scootaloo and RD are a great pairing not only because they make sense together but because they both have an incredible amount of tenacity. RD struggles with learning how to provide care and support to somepony who, in a lot of ways is just like her, but who is also hindered by a disability far different from anything Rainbow Dash has ever experienced herself. While Scootaloo struggles with her ability to be just like Dash even though sometimes she forgets having heart is more important than having wings. Their determination or tenacity to be exactly what the other one needs is what drives them together. They're two ponies determined to make each other happy even if it takes entire life time of dreams. And that's why they are so beautiful together. I wish the writers would go deeper with these too. Truly a pairing that the fans need to see more of in S5!