There are a few things that are working here. First the temps that you are keeping her may or not be to low for her. If she is a aussi snake neck(Chelodina longicolis) then that temp is kind of good for her(but even then considering that she is a baby and high temps only are harmfull for adults in the long term I recomend that you raise the temp to about 24 C). If she is any other snake neck then that temp is way to low. For new guinea and indonesian species the ideal temp is 26-28C. Then there is that softening thing. The fact that she is sheding can one of mean 2 things: one your turtle is a healty one and she is just sheding its old shell ceratin skales or your turtle has calcium deficiency and because the bone behind the ceratin layer is deforming and recessing , the skales fall. I see this all the time whit mass imported baby turtles here. Because you say your tutle shell is going soft I think is this what is going on.
For what you say I think the diet you are ofering your turtle is still kind of poor. Forget that calcium block thing, Ive tryed and has never worked, its just one of thouse market things. The fact that your turt is already ill tells me that she has not toched that. The shrimp you are using its fresedryed? If is cut that out as well. Even if that contains some calcium is a very poor food choice, lacks vitamins and has been associated with infections and calcium and vitamins deficiencys on baby turtles. Turtle tucker is also just a snak and not something I would offer to a ill turt like yours.
Insted insist on calcium rich foods like one of the top turtle pellets like tetra reptomin, mazuri and zoomed´s. Varieds frozen fish foods are also very good like daphnia, mosquito larva, the bloodworms you are using, artemia ,krill,etc. One of the good ways to get calcium and vitamins in your turt is to get a chunk of chicken,turkey,etc, shred him very finely in a mash and then ad a good multivitamin and mineral powder (like zoomed´s reptivite) to it. Make also shure you have a good UV lamp of 5.0 uv (like reptisun of zoomed )and that there is nothing between your turts and the lamp (plastic, glass,etc) Dont also forget that the lamp must at a maximun distance of 12 inches of the turt in order to work and that this lamps lose its eficiency in about 6 moths.
Finely I would separate your 2 turts. It is higly not recomended to keep together turts that dont meet in the wild. Microorganisms that one turt naturaly has and that dont do any harm to him may prove very harmfull to another. Make shure to fix that
