Sussex19
Free Ranging
I'm thinking she could well be going broody.Link to Penny
If you see her like that again, you could try reaching under her from the front with one hand.
See is she does a kind of shuffle, drawing your hand in and up, once your hand is fully underneath
This is my personal favorite way of telling if hens are broody, and I have found it very effective.
(the shuffle is to gather up the eggs, that she thinks she has under her)