@Masem
Exactly this. I think it’s easy to forget the amount of energy involved in spacetime manipulation, magic or no magic. I could go on a long rant here about General Relativity and the multitude of reasons why we likely will never harness wormholes or similar for interstellar travel, but suffice to say, teleportation is likely extremely complex and energy-intensive. I think I’ve read a few stories on Fimfiction that delve more deeply into realistic ways the spell could be structured (not counting Blink and its derivatives).

@AC97  
Good points.

 
Assuming Twilight taught her the fundamentals of teleportation during some variant of “Twilight Time” at some point, then I’m sure that she made sure to drill in a few things about safety regarding doing it with passengers, in contrast to how it seemed to be with Twilight.
 
Remember, Ticket Master was the third episode of the first season, and Twilight seemed to first learn teleportation after Nightmare Moon subjected her to it once, in the previous episode, and she seemed to bring a hoof to her head afterwards, and took a notable amount of time charging up a teleport at that time, as if she wasn’t used to doing it at all, hence why I think she learned it on the spot. (Being that inherently good at copying magic is kind of Twilight’s thing, like how she copied Starlight’s spells after seeing them or experiencing them once [her shield spell, and her crystallization spell])
 
As far as teleporting into a hay bale, that’s pretty good for a beginner. It seems like her stamina could use some work (probably goes with training), but her magic indeed looks like it has some promise, like it did two seasons ago.

well is normal after thier First Teleportion! but after a lot of training is no longer a problem but of course every unicorn got thier limite of number of teleportion can do in one day or in less a hour!

@InuYugiHakusho  
But I just can’t fathom why a pony that does frequent trips to pick up supplies/restock/make deliveries(at least to the post shop) and needs to essentially be two places at once at times wouldn’t want to pick up a spell like that.

@Masem  
Makes sense to me.

@mjangelvortex  
In my headcanon, teleport is a “powerful” spell that takes lots of practice and magical power to use (in contrast to their everyday “cantrips” like “light” and “light levitation” that all unicorns can do w/o significant training). So Twilight had to learn to teleport to the point that she can teleport spam, teleport several ponies, teleport long distances, which is also something Starlight learned.
 
Sweetie may have learned personal short-distance teleporting from Twilight, but this may have been her first shot at doing it with a passenger, making it difficult and headache-inducing.

Sweetie Belle used Teleport!
 
Sweetie Belle is damaged by recoil!

I recall other unicorns getting minor headaches after teleporting. For example, Twilight and Spike were dazed for a bit after teleporting in The Ticket Master. There were other cases of it happening I think but I forgot which episodes it happened.

@PaintEdits  
Or Trixie.

Neat details

@PaintEdits  
Sweetie Belle learned levitation magic from Twilight, who regularly uses teleportation magic. It’s likely Twilight taught Sweetie the fundamentals, but warned her not to use the spell until she was older, as it appears to be physically taxing.

@Inkan1969  
Also that her horn fizzled and she appeard to have a slight headache after doing it. Shows that it must have strained her in some way.

Also, the detail that she wound up inside the hay bale. She still can’t do this correctly: she’s lucky she didn’t teleport into a wall, or she didn’t fuse with the hay.

Just to be clear Rarity’s never used teleport, but Sweetie has?