Most cones (like what they use for dogs and cats) are made from plastic, so I wouldn't feel great about using one on a chin even if it did come in the proper size. She'd probably just chew through it, potentially harming herself in the process.
My guess is that she's chewing it because it itches. When wounds heal and start to scab over, they often start to itch something awful. I've even re-opened some healing wounds of my own because I couldn't deal with the itching and ended up scratching the hell out of it (sometimes in my sleep). I'm one of those people who has like zero tolerance for itchiness, haha. I scratch mosquito bites until they bleed, because I'd rather they hurt than itch. So I can relate to your chin!
You could ask the vet for some anti-itch ointment and see if that helps (something like hydrocortisone often works well on humans and larger animals, though I don't know if it's safe to use with chins, so definitely check with your vet, don't just go out and buy some). If you do get something to help with itching, you'll want to apply it primarily to the edges of the wound, as that freshly healing/regenerating skin is usually what itches the most.
If anti-itch ointment is not possible or doesn't work, the only thing I can think of would be to try to make some sort of collar out of anti-pill fleece, since that's one of the only "chin-safe" materials (outside of certain woods). It doesn't unravel, so it doesn't pose the same risks when chewed as other fabrics (or plastic, which can come apart in jagged pieces). Only issue is that it's not at all rigid, so I don't know how effective it would actually be. Still, it might help if you made it long enough, though she may struggle to eat with it on, so you might have to either hand-feed her or remove it (with close supervision) a few times a day to let her eat on her own. Or maybe you could sew some stainless steel wire into it to make it more rigid? I dunno, just spitballing.
Maybe someone else who has dealt with a similar situation will have some better solutions to suggest, but those are the only ideas I can come up with.
