I would increase the calcium intake with a powered supplement like RepCal (not Reptocal, which contains phosphorous). To keep it on the pellets better, I would moisten them first, put on the powder and handfeed her if she will let you. I`d also give her the softened bones of fish like sardines and salmon (packed in water not oil and cleaning and rinsing them well before giving them to her). I`ve never heard of chalk in water (plaster of paris, yes, chalk no), but don`t think even if it is OK to do so she would get enough that way to make a difference. I`d also have cuttlebone in the tank in case she wants it.
As far as lighting, since you have turtles already you probably know this, but if you don`t go to http://www.tortoisetrust.org/articles/lighting.html and scroll down to the picture of the ZooMed lightbulb with the iguana on the front. This is what you do NOT want--it does not provide UVB rays. (The whole article is really good to learn about lighting.)
I`ve never heard of a UVB light costing $7.00--about the cheapest I`ve heard is the ESU UVB coil lamp for around $20.00. If the package doesn`t say UVB, don`t get it, even if it says it`s full spectrum.
If you can, I`d also take her outside for some unfiltered sunlight several times a week (the best for the UVB), as well as making sure she`s getting an otherwise balanced diet.