Hello Lornatrae!
What does she get for food other than hay? If she is getting more pellets or veg than usual she may be filling up on those instead. Also, when my bunnies were recovering from a neuter or spay and didn’t seem interested in hay, I sprinkled a teeny bit of alfalfa hay over their regular hay, which got them digging in the litter box. Then once they were there, they seemed to realize that they liked some of the other things in there as well!
Have you changed her litterbox or litter? I jst changed my litter brand yesterday, and one of my bunnies who was perfectly litterbox trained peed in the corner of my room because she didn’t understand the new smell of the box! A new box or a new smell can discourage them from getting in the box and eating the hay.
I’m in the US myself, but there are lots of UK members here, I’m sure one will be able to tell you where they get the cubes!