Do you have other SS of her breed or just her? SS eggs are pretty recognizable due to pale tan and the medium size. It's important to note when she lays and what the quality of the shell is.
When a hen heads to a nest it's because she is feeling the sensation of an egg coming down her oviduct, and she remains on the nest for as long as this pressure sensation remains.
It's doubtful she's got an egg stuck, but it is possible the egg is shifting in the oviduct and perhaps risking getting dumped out at some point into her abdominal cavity. When this happens, it's called internal laying. Hens do not survive this for long.
None of this can be helped. You can only intervene if, by lethargic behavior, the hen gives indication she's become egg bound. At that point, you can administer a calcium supplement to stimulate contractions to help her get the egg out.
If this behavior has only recently been occurring, it could be attributed to end of season drop-off of egg laying if you are located in the northern hemisphere. Hens can have irregular laying habits as they approach molt.