@The Equestrian Zodiac
And they didn’t wear costumes when they were seen in the show. If “this filly” would have shown up anywhere else than at a Daring Do convention and without a costume, I would immediately think she’s Peach Fuzz’ twin sister who wears her mane and tail differently and who dyes them in a different color, so she can be told apart from Peach Fuzz. And start to come up with theories why they have the same cutie mark and what that means.
But since it was at the convention, where every attending pony was wearing some sort of Daring Do cosplay, the different mane and tail, in combination with the rest of her look, make clear that they’re part of the costume and just wigs.
And, as cheezedoodle said under the screencap he uploaded of Peach Fuzz in her cosplay, the mane and tail look just as messed up as the shirt and the helmet, so they’re part of the costume and are so messed-up to meet the general style/theme of it.
There is not really something that indicates this could be a different filly than Peach Fuzz.