@Mayojar77  
Magic comes easy to her not only because she’s talented but because she studies and practices constantly.

More like complacent. Sure, it’s the easy route, but it’s also the best route…
 
None of the ponies really embody any of the sins as they’re supposed to be balanced characters, not one-dimensional caricatures, so no matter how you match them there’ll be issues. I’d say OP did a fair job.

@Background Pony  
The thing is, most spells don’t even strain Twilight, and there’s only a few episodes where she struggles, and it’s because of the scope of the spell she’s casting. Because magic comes naturally to her, she is lazy for resorting to it all the time.

@Mayojar77  
Casting magic is still exhausting with particularly complex spells. After all it’s her talent, you can’t blame her for focusing on it. One could argue that studying and learning is a form of non-physical work.

@The Twelfth Doctor Whoof  
She “flirted” with the dragon to get his pile of gems (which would be greed), and she fantasized about marrying Blueblood because she wanted to impress everyone and become royalty. Which would be greed too, not lust. Whereas Spike goes gaga eyed over Rarity every time he lies eyes on her. Tell me why lust wouldn’t fit him if it fits Rarity, and way better as well.

@The Twelfth Doctor Whoof  
I say Sloth. Twilight always solves her problems with magic, and the one time she’s not allowed to use magic to solve her problem, someone else solves it by giving her a desk job.  
Hell, they wouldn’t have needed her help that year if she wasn’t so intent on trying out every single job.

@Background Pony  
Did you not see “Dragonshy” and how Rarity reacted during it? Did you not see “Best Night Ever” where she wanted to bone Blueblood (before finding out he’s a raging douchehole)?
 
All of these fit pretty well, except for Twilight as Envy, and that’s only because none of the seven particularly fit her and she needs one.

@Perteks  
Soo…wouldn’t that be greed?

@Background Pony  
Because she went after money and fame

Why is Rarity lust? Because she’s an attractive confident female? God forbid that equates to being the horniest of the main cast. Spike on the other hand, who dreams about and drools over Rarity constantly is a better fit for that.
 
And AJ is proud, but mostly stubborn, and Twilight is flatout arrogant sometimes when it comes to her abilities and position. It’s a better fit for her, or even sloth like Kippers said.

@The Floor Kippers  
That fits a little better.  
Twilight always resorts to magic (read; the easy way) to solve all her problems, and Rainbow wants to live the life of her idols.

@Itsthinking  
Normal Spike also lusts after Rarity and Normal Rarity can be greedy.
 
I’d also switch Twi and RD.

@The Floor Kippers  
Nah, those kind of fit. Even normal Spike has some generosity and normal Rarity some greed.

@HamburgerTime  
I’d switch Rarity and Spike.

The Elements of Sin

I’d switch AJ and Twi.

@RaineV1  
She’s also has to take those breaks, otherwise every other Pegasus in Ponyville is out of a job.

I can’t see Dash as sloth. She naps often, but she also trains hard.

Hmm. This actually more or less fits.