Congratulations on having her for this long! It really is pretty amazing!
As for this bump... Only a vet would know for sure, but i had a male Veiled chameleon who developed somethign similar in almost teh exact same spot (only more on his right side), in between his eyes (he is only two).
I took him to my vet and they did a needle aspirate, and although hes not a reptile specialist, he said it looked like an abscess from what he could tell form under the microscope, full of white blood cells and bacteria.We ended up lancing it and trying to get as much gunk out that we could (he was DEFF not a happy camper!!) and he gave me some drops to keep putting on it... After lancing, it ended up scabbing over, and eventually, after a couple of months, healed over with scar tissue and is about half teh size it was at teh start... My guy never bothered at it, although he did seem alittle uncomfortable with the drops.
I would recommend taking her to the vet to at least get an aspirate done, because that will tell you the most.
Best of luck!