Simple thread: Who do you think Rainbow Dash's mother is? Why?
Where is she when Dash is growing up? When Dash is an adult? What relationship do they have? How do Mommy and Daddy get along?

I think Princess Celestia is Rainbow's mother. I'm calling on her magic for this.
What is the Sonic Rainboom? An explosion of light and a burst of rainbow colors, with a rainbow following her shortly afterwards. This is not a scientific event, but obviously a magical one.
No-one else has been shown to do one, not even the Wonderbolts, presumably with the fastest pegasi around. Perhaps the Rainboom has nothing to do with speed but is entirely magical? She was screaming through the air when she did one as a child, but she didn't catch up to Rarity and the Wonderbolts too quick in Cloudsdale. And at the wedding she was heading straight up, it didn't look that fast either.
Why would a single pegasi, as fast as she is, do something so incredible that faster ones can not, and at different speeds? We know Twilight did something similar to a Sonic Rainboom within days of getting her wings, and she has a great deal of magic. And who was the last one anyway?
Maybe someone with untold magic, like a certain Sun Princess? With rainbow hair herself? Very similar colored eyes?