@Beau Skunky  
My headcanon for why Tiara’s mom is gone actually ties into your headcanon on Rich being a workaholic: Tiara’s mother grew tired of the fact that Rich seemed to be more concerned with his career than with his family and their marriage (the usual tropes of forgetting/not showing up to birthdays/anniversaries apply here) and ended up divorcing him. Unfortunately, the courts left Di in Rich’s custody because they believed she’d be more economically secure in his hooves than in those of her mother’s. I’m thinking Di only sees her mom once a month, but on those days she behaves like an entirely different pony.

@Crystal Neighybánya  
Perhaps, though I prefer the idea of him being a nice guy who doesn’t necessarily have time for her, and unintentionally kinda neglects her. (Like that first headcanon you regarded.) He probably makes up for it by giving her whatever she wants, therefore Tiara becomes a bit bratty, but secretly does desire more attention from him. (Therefore it’s never enough.) Being raised by her butler almost sounds plausible, seeing how we sometimes see her with him more.  
And ironically, Filthy probably works to hard, because he wants to make sure she has a good life. He’s not a bad guy, but probably doesn’t know how to be a parent very well, especially sense it seems like her mother might be gone.
 
She might’ve also gotten her “snobbish” traits from bad influences from school, and such.

@Tetrominon  
Bad grades?

Sailor Spoon! <3
 
Incoming Filthy Rich Headcanon: He’s a nice enough guy and a decent enough businessman, but he’s not really cut out for fatherhood and tends to leave Diamond Tiara in the care of Randolph as opposed to parenting her himself. Because Randolph is contractually obligated to do whatever Diamond Tiara asks and Filthy Rich only ever seems to intervene when she gets in his way or threatens his business dealings, she’s been running hogwild.
 
@Evowizard25  
If that’s the case, then keeping her in public school would run counter to that. If you’re a big fish in a small pond, it’s a whole lot easier to start thinking you’re all that and a bag of chips than in if you’re in a school were your wealth and status are the norm, rather than the exception. It’s more likely Rich doesn’t want to shell out the money to put her through private school.
 
@Beau Skunky  
But Di had to get her less savory traits from somewhere - her father’s as good a place as any (atleast until Di is given a mother/her mother appears). He doesn’t necessarily have to be a clone of Di (that would just be silly), but maybe he’s got a bit of an ego, maybe he’s a bit vain or perhaps he’s a bit on the greedy side. It’s not like this would be out of the ordinary in a show like MLP, either: Angelica Pickles - for example - clearly got some of her behaviors from Drew (and Charlotte - but again, Di doesn’t seem to have a mother).

… but she’s still a bitch.

@Tetrominon  
Maybe they preferred going to school where their wealth and status are exceptional, rather than being the average.

@Tetrominon  
I don’t know even in that ep’, Filthy still seemed nicer then he was portrayed in the comics. >>856683 >>896654
 
I prefer to think Filthy’s an honest businessman, and isn’t automatically “evil,” just ‘cause he’s “loaded.” (Especially, sense he’s friends with the Apple family.) Plus I like how that contrasts with his daughter “not being as nice.”

@Evowizard25  
Yeah, that sounds like Filthy’s kind of thinking. (When he’s not written by Scott Sonneborn, anyway.)

@Tetrominon  
It could be that her father didn’t want her to grow up thinking that she’s ‘better’ than everyone else. That she’s just as important as the common man{pony}. Honestly, it would have definitely gone to her head if she was sent to a special privileged school. That and make some true friends.

@Registered Anon  
fun, parties, etc :/

And on that day Silver Spoon found her fetish.

@Tetrominon  
Maybe the idea of Crystal Prep didn’t come until after the first Equestria Girls came out.

Hey, it just dawned on me… how is it neither Tiara or Spoon are attending the big exclusive prep school that’s apparently just on the other side of town?!