Live or dead mouse?
I do not know if a mouse is okay for food. But it seems that turtle can eat a variety of foods. I only wonder about the harder parts of a mouse such as teeth.
Where and how did you get the mouse? If it was dead, then you need to know what caused it's death. If it was poisoned, then that poison might now be in your turtle. If it was disease, it might be transferable to your turtle.
The length of time a food source is dead is important. It breaks down and is infested in various ways.
I have no idea what might have been bad about it. Or how to treat it. But I hope it passes and your turtle survives. In the future, know all about what you feed your pet.
I hope all goes well.