You mean for the lights? The UVB light should be as long or almost as long as the cage. my cages are 24" wide, and my bulbs are 24" inside a 30" hood. It hangs over a little. I could have used a 24" hood with an 18" bulb as well and that would have fine.
Since you're using a CFL putting it under the dome would work, unless you want to go get the ReptiSun 5.0. If you get a screen cage you'll need a regular household incandescent bulb and the UVB, so that your chameleon can bask and get UVB from the one light and heat from the other.
If you put her in an adult size cage at this age, you should cup feed her and not free range the crickets. The adult size cage might be too big for her, she is quite tiny at this point. I haven't kept a chameleon that small yet. I keep mine in screen cages from LLLreptile.com They have smaller cheaper ones that you could start her in now and then get the full sized one later, and use the smaller one as an outdoor cage. The price for the two combined without shipping would probably be less than $135.
Did you remove the substrate from your cage yet?