"They reach sexual maturity within four to five months, at 8 to 12 inches long"...
http://nationalzoo.si.edu/Animals/ReptilesAmphibians/Facts/FactSheets/Veiledchameleon.cfm
"Veiled can reach sexual maturity very early, some authors report as early 3 1/2 months"...
http://www.kingsnake.com/rockymountain/RMHPages/RMHCarpets.htm
You'll have to scan down a long way to page 20 for this quote...
"Female veiled chameleons generally reach sexual maturity anywhere from 4 1/2 to 5 months but, the occasional female may become ready as early as 3 1/2 months "....
http://www.albertareptilesociety.org/bulletin/taras.2004.1.pdf
If you leave the sand out and you don't recognize the often subtle indications that the female needs to lay eggs you risk her becoming eggbound.
Handling a female...moving her back and forth from the egglaying bin to the cage also increases the risk of eggbinding (stress) and if it hasn't happened to you yet I would say you are lucky....
See page 1668...
http://www.ivis.org/proceedings/navc/2006/SAE/603.pdf?LA=1
Also...laying clutches of more than 2 or 3 dozen will more than likely increase the risk that a female will die young.
Overfeeding a female veiled (which contributes to larger clutches) can also push the chameleon towards MBD and eggbinding...
"Excessive feeding and lack of calcium, and lack of a suitable egg laying site are all thought to contribute to eggbinding in veiled chameleons".
If your female is eating the sand while the container is in the cage, there is nothing to prevent her from eating it when she is moved to an egglaying bin IMHO.