You said..."She's kept in the window , but only gets brief direct sunlight"...exposure to UVB allows the chameleon to produce vitamin D3 which allows it to use the calcium....but UVB from artificial means or from the sun must not pass through glass or plastic.
Phosphorous, calcium, D3 and vitamin A are four of the big players in bone health (and they play other parts in the body too)...so they must be kept in balance. Its important to look not only at what the insects contain, but at what supplements you are using and what you feed to the insects and gutload them with.
Appropriate basking temperatures are important for good digestion which plays a part in nutrient absorption.
Feeder insects usually have a poor ratio of calcium to phosphorous, so dusting them with a phos.-free calcium powder helps to make up for this.
Vitamin A from beta carotene sources can not build up in the system, but those from preformed sources can. However, there is controversy about whether all chameleons can convert beta carotene into vitamin A, so it may be necessary to provide a little preformed from time to time. Excess preformed vitamin A can build up in the system and prevent the D3 from doing its job...and lead to MBD.
Excess D3 from supplements can also build up in the system and lead to problems....but not enough will mean that not enough calcium can be absorbed.
If your chameleon has MBD caused by lack of calcium, then a vet can give it shots of calcium until the blood calcium levels are high enough to give it a shot of calcitonin which will rapidly draw the calcium back into the bones. (The blood calcium levels have to be high enough or the blood will be left short of calcium and the chameleon may die.)
Whatever damage (breaks, etc.) the chameleon has already sustained will likely remain...but if treated early enough, a chameleon can live a fairly long life.
