Did you actually put her on the roost... after full dark so she can't see to get back to nest??We go in there when we lock up and push her out but she just returns after we've left.
Did you get all your birds at the same time?
She may be low in the pecking order.
Looking forward to seeing your set up.
It would have to be tilted at such a sharp angle(more than 45°) not a good idea for a nest.If I tilt the floor of my current nesting boxes would that encourage her to sleep somewhere else?