OoP: Petunia, expelled?

[Erin]

No: HPFGUIDX 64597

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I'm germinating a theory I'd like feedback on, if anyone would like 
to help me...or blow it out of the water, take your pick.

I theorize (get ready) that Petunia is...a failed witch. I theorize 
that, just like her sister, Petunia recieved the Hogwarts letter and 
shipped right off, pleased as punch. I also theorize that somewhere 
along the line, something went bad wrong and Petunia was expelled, 
had her wand snapped, and was sent packing from the WW for the rest 
of her life. 

Expelled, you say? It sure seems to happen pretty easily. Hagrid was 
expelled on purely circumstantial evidence. Harry was nearly expelled 
for performing underage magic twice. I realize these things both 
happened in times of panic, but given the amount of scary things that 
go on when you're dealing with magic, the closemouthed nature of 
wizard culture, and the state of wizard justice, I'd say it's not 
altogether impossible.

It also seems odd to me that one sibling should turn out to be a 
witch and not the other. In every sibling relationship mentioned, 
*all* of the siblings are magical, even in Muggle families. I believe 
the Creevys are Muggleborns, correct? We don't know the Patil girls' 
background as far as families go, at least, I don't think we do, but 
they're both magical as well. The only Muggleborn sibling 
relationship we know of where one sibling is a Muggle is Lily and 
Petunia, AFAIK. 

If Petunia did spend a small amount of time at Hogwarts, it would 
explain her specific knowledge about Dementors. After all, she knew 
their *exact function*, not just that they were something creepy that 
Lily, James, or X "awful boy" (I'm not fully convinced that phrase 
refers to James) mentioned in passing. She also got the name of the 
wizard prison absolutely correct...notice that Vernon can't even 
recall Voldemort's name, and he killed his in-laws.

Being expelled from Hogwarts, especially if the justification was 
shaky, would've given Petunia an enduring bitterness toward the WW, 
and especially toward her sister, who went on to become not only a 
success, but a heroic martyr. Imagine having a taste of something 
really wonderful, then having it taken from you. Then imagine that 
your sibling comes prancing home from school showing off her mad 
skillz, waving her wand around. Wouldn't that just *burn*? It would 
certainly give her incentive to be awfully jealous. Imagine, too, 
that you're stuck with said sibling's offspring, who could 
conceivably go off to Hogwarts and come prancing home showing off his 
mad skillz, waving his wand around. Wouldn't that give you a desire 
to stamp out all signs of magic in the kid? 

Given all of this, I also theorize that Petunia is our girl who will 
develop magical talents late in life. If she is a witch, imagine what 
she could do with all of that pent-up emotion, if they gave her a 
wand and some proper instruction. That would make for a nice role-
reversal, if Harry was put in charge of tutoring her. Better yet, if 
Snape was! I'd like to see those two in a room together ;)