I agree. The use of antibiotics should really only be to treat an infection, and your vet hasn't found anything wrong so I would just do w/o medicating her until there is an actual reason to medicate her. She does also look gravid. Like Kinyonga said, she'll need a proper egg laying bin in a secluded spot in her cage where she can feel safe and secure while she's digging her tunnel and laying the eggs or else she won't lay them and could become egg bound.
Also the sneezing could be her trying to expel salts from her nose. She shouldn't do this often, though. And a frequent sound of sneezing or popping sounds coming from her mouth could indicate an RI but this doesn't appear to be the case here. She hasn't shed in a couple of months and might just be getting ready to shed and is why she's slowing her activity down. You might even see her go w/o eating the day before she breaks the shed. This isn't something you should worry about, and is common thing that chameleons in the shed process do.
I would also say based on the pic of her cage, it's perfect w/ a good amount of live plants and cover, however, you might want to add some more branches in the middle for her.
Please fill this form out though so we can dive deeper into her care. Females are a bit more difficult to keep than males due to the egg laying process, but are so much fun to keep when you have everything right for her in her habitat. They can also be a nightmare once the health issues start occurring if you don't have your husbandry on point so lets just take a look at that, overall while we're here
