It's pretty clear that Rey depends on her speeder for her livelihood as a scavenger on Jakku. The Star Destroyer that she's seen climbing through is clearly some significant distance away from Niima Outpost: she exits the ship at midday and it's almost sunset by the time she arrives at the outpost. Her AT-AT home is much closer to the outpost than the ship but still farther than can be easily traveled on foot. Also, Rey's home is close enough to the village of Tuanul that BB-8 was able to make it from there to the AT-AT in one night.
There's a map in the new Star Wars: Galactic Atlas factbook. It is, alas, not to any sort of obvious scale, but it does at least show you where your four locations are in relation to each other.
As to why it took Rey so long to get back, you might want to note that she took a complete lap of a nearby attraction called "The Sitter", presumably looking for good salvage on her way back.