Okay, I can't answer as to why she's doing this, but I can point out a few things that need improving. When a turtles habitat is not up to par it can affect their health. It sounds like Daytona is sensitive to this fact.
1) A 10 gallon tank is too small for one hatchling let alone two. Minimum recommended size is 10 gallons per inch of turtle. And remember that their home needs to grow as they grow.
2)Knowing exact temps and keeping correct temps in their environment is vital to their health. Water temp should be a constant 78 degree for hatchlings with a basking area temp of 88-90. (lights should be on a day/night cycle so basking temp will only remain this during day)
3)Never feed spinach. It contains oxalic acid that blocks/prevents them from absorbing the calcium in their diet. This will lead to Metabolic Bone Disease.
4)Using Vita shell can damage their shells greatly. It blocks the shell from breathing and can cause major shell damage when used over a period of time.
5)I've heard that feeding some types of shellfish can cause harm to your turtles. Some shellfish carry a bacteria that's been linked to shell rot. I'm not sure about shrimp, but feeding it raw is not a good idea and freeze-dried shrimp should only be used as treats around once a month due to the high protein content.
This probably isn't complete and others will be along to help as well. But please take time to read through the main site and the forum as much as you can. If you have any more questions after reading just ask.
