Is there any canon support to know whether Petunia Evans had any magical ability at all? Obviously, she had almost none otherwise she'd be accepted to Hogwarts.
But it's hard to believe that she had precisely zero, being Lily's sister.
Science Fiction & Fantasy Stack Exchange is a question and answer site for science fiction and fantasy enthusiasts. It only takes a minute to sign up.
Sign up to join this communityI think the only thing that would demonstrate Petunia had some sort of fortitude (I hesitate to call it magic, because I think one is either magic or they're not) is that she managed to get a letter to Dumbledore at Hogwarts as a child. Dumbledore wrote back a very kind letter to Petunia, but it must have somehow ingrained in Petunia that she was not magical while Lily was. And her bitterness built accordingly.
‘Severus saw the envelope, and he couldn’t believe a Muggle could have contacted Hogwarts, that’s all!’
‘Apparently wizards poke their noses in everywhere!’ said Petunia, now as pale as she had been flushed. ‘Freak!’ she spat at her sister, and she flounced off to where her parents stood ...
Deathly Hallows - page 538 - Bloomsbury - chapter 33, The Prince's Tale
I do not believe Petunia is magical and aside from what I wrote above I don't believe there is any canon information to indicate otherwise.
What if she's a Squib, though? A Muggleborn Squib. Is that even possible? ETA: Petunia's not a Squib. I happened to find this question and answer while looking for something else:
Is Aunt Petunia a Squib?
J. K. Rowling: Good question. No, she is not, but — [Laughter]. No, she is not a Squib. She is a Muggle, but — [Laughter]. You will have to read the other books. You might have got the impression that there is a little bit more to Aunt Petunia than meets the eye, and you will find out what it is. She is not a Squib, although that is a very good guess.
EDINBURGH BOOK FESTIVAL - AUGUST 15, 2004 - BLOOMSBURY
Petunia's a Muggle.