You said...the last one you had showed signs of MBD (spine was curved, tail was kinked, and she had a hard time getting around, using her leg to grip her side, a bit clumsy) after only being with you for 3 weeks....if there were no signs when you bought her, then its not likely anything you did that caused it in such a short time. Her legs look fine in the pictures but the things listed in the bracket above can be symptoms of nutrient imbalances. It doesn't have to be just a lack of calcium but could be an imbalance between the calcium, phos., D3 and vitamin A.
You said that the sister of the one you had was already producing eggs at about 4 months of age...and you said..."I want to find good supplements not medicines, but whatever they are giving is not enough for a baby"...if she was overfed and grew rapidly this could have led to an imbalance in nutrients too.
BTW...if the veileds are not overfed constantly they will produce smaller clutches as a rule...and that should lengthen their lives.
You said you use Flukers Phosphorous free Calcium and D3...since many/most of the feeder insects have a poor ratio of calcium to phos., its important to dust the insects at most feedings with a phos.-free calcium powder to make up for it.
I dust with a phos.-free calcium/D3 powder twice a month to ensure that the chameleon gets some D3 without overdoing it. I leave them to produce the rest of the D3 from their exposure to the UVB. (The UVB shouldn't pass through glass or screen...and some compacts, spirals can cause eye problems...but there are no bad reports against the long linear fluorescent Repti-sun 5.0 UVB bulb.)
I dust twice a month with a vitamin powder that contains a beta carotene source of vitamin A. Beta carotene (prOformed) source of vitamin A will not build up in the system, but there is controversy as to whether all/any chameleons can convert it so some people give a little prEformed once in a while. Excess prEformed may prevent the D3 from doing its job and push the chameleon towards MBD.
Calcium, D3, vitamin A and phos. are all important players in bone health and other systems in the chameleon and need to be in balance. When trying to balance them you need to look at what you feed the chameleon, what you feed the insects and what supplements you use.
Temperature also plays a part...good temperatures aid in good digestion which plays a part indirectly in nutrient absorption.
Gutloading is important...you can gutload crickets, superworms, locusts, roaches, etc. with a wide assortment of greens (dandelions, collards, kale, endive, parsley, escarole, etc.) and veggies (squash, zucchini, carrots, sweet potato, sweet red pepper, etc.)
You said you have an infrared heat lamp and a drip system...for heat I (and many others) use a regular incandescent household bulb in a dome hood. The wattage depends on the temperature the light makes in the cage. For hatchling veileds I keep the basking temperature in the low 80's. I also don't use a dripper for a hatchling..they can aspirate the water if the drips are too large.
The main concern with substrates is the risk of impaction. Why take the risk?