They all look female when young. Might have been incubated at a particular temperature and then it has a greater likelihood it has a greater likelihood of being the sex that they were going for. But this young, short of a blood test, you're not going to know
I would get her checked but just so you guys know, while allergies are very rare in some species they are never impossible. With tortoises there has only been one medically confirmed case of an allergy as far as I know. See this article...
When I was 14 I had a turtle go 5 days between laying in the water and using the nesting area I provided after. Also, it is always possible she laid more than the 1 in the water and ate them.
I 2nd doing something to make the area warm. Mine have always preferred a nice warm outdoor space for laying. For an indoor space that looks pretty good. Maybe put some artificial plant or something in a corner so she thinks she's got a hidden area if she doesn't take to it.
Has she ever been around a male, if so when? She needs a place where she can dig otherwise she's not going to want to lay even if she needs to. Many turtles will still lay eggs even when they haven't been around a male and it can't be fertile. If she laid it in the water I can pretty much...