I have seen some ‘popcorn’ treats for bunnies as well that are sold in leading pet shops. Granted, not everything there is great for them but I think that if it was overly toxic, they’d not sell it. Still though, I’d not let her have her fill of a bag of the stuff. Maybe one or two puffs every other day or so won’t hurt. I’d also say that if you pop your own (free of all oils and other additivies), it would be a bit better.
I believe the danger with corn is that dried corn kernels have husks that they cannot digest and therefore can cause issues. So if you are going to give a bun popcorn, make sure it is nothing but the white stuff (remove the left over kernal bits on the ‘bottom/inside’ of the puff.
Mine loves Ritz crackers and Sun Chips and, although they aren’t good for a bunny, she’d receive about half a cracker or chip occasionally (once a week) and she’s been just fine. Just remember that their systems are hyper sensitive compared to our digestive tracts.
They can be so hard to resist with their cute lil whiskers…