well she’s HALF right. Perfect speed… is being ANYWHERE.

I’ve always thought that her teleportation worked like G1 winking, so she couldn’t teleport out of ropes.
 
In Dragon Quest, it didn’t look like she reached Ponyville to me, she just went to the edge of the forest she was in. That shot doesn’t have any part of Ponyville in sight, so saying that she took them that far is kind of a stretch.
 
At any rate, that jump took a lot more effort out of Twilight than most, though whether that was from distance, transporting a group, or from setting it up from moving is unknown.

Well she did also teleported herself and spike accidentally back in the library once. Which wasn’t in eye side at the moment. And she teleported Pinkie Pie there too. Without her knowing.  
So yes there aren’t any established rules. Just the ones for plot and comedy.
 
Otherwise they could teleport to Canterlot, instead of traveling with the train…  
A bit strange.

In my headcanon she can only teleport to places she could’ve walked to, which is why she can’t teleport into a closed room, or over a chasm.
 
When it comes to distance, my guess is that she is capable of teleporting a few blocks in Ponyville.
 
Canonically there are no real rules and her abilities in teleporting vary depending on the plot. She teleported from the Dragon Land to Ponyville with Spike and the others at the end of the episode afterall.
 
Also, teleporting isn’t instanteneous. There is always a delay. I’m not sure if it is dependant on the distance though.

Not very far, as a rule. Usually, less than a hundred yards.

How far can she teleport anyway?

I remember some statistic sheet a good while ago. People wondered why RD had a speed of 8 while Twi had a speed of 10.
 
THIS is why.

^what?

Almost had a koan going there.