Hi there, you are through to Dr. Jake. Im a UK based vet. im sorry to hear of your concerns with your turtle, Gina. we see shell problems occur in turtles. this can often be due to trauma which has led to damage, or it can be due to husbandry issues such as poor water quality and poor nutrition leading to softening of the shell which predisposes trauma and or infection.
water quality is important as turtles are generally messy animals so make sure there is a strong filtration system available to combat the high levels of faeces and spoiled food they drop in the water, water testing kits are available - generally using topical fish kits can be useful to monitor toxin levels such as ammonia, nitrate and nitrites which should be kept low to prevent damage to the shell.
shell damage can be due to soft shells or poor epithelial layers of the scales/ skin. it is important that correct ultraviolet lighting is provided to allow for adequate calcium absorption and vitamin d3 production. this should be complimented with appropriate vitamin and mineral supplementation , vitamin A is particularly important in turtles to prevent skin and ocular conditions.
for this, i would recommend making an appointment with a local vet who has experience with reptiles, they will be able to provide a clinical exam and assess the shell, they will be able to provide appropriate medications if the shell is damaged, this may require antibiotics to prevent or treat infection. also dry docking or partial docking your turtle may be required to aid healing of this. these can take a while to heal so please be patient as these areas are generally slow to heal.
i hope all this information helps