What kind of hay has Lucy tried? Devon and Amber love orchard, timothy, and oat hays. We get ours from Oxbow. Oxbow is a US company though, so I'm not sure if they ship to the UK. But regardless, maybe try giving her some different varieties of hay.
Sometimes rabbits get picky about certain brands or even certain bags of hay. You might need to try a different brand or a different lot of bags to find some she likes.
For dried grass, are you talking about that Readigrass stuff? We don't have it in the States, so I've never used it before. If you're thinking of lawn grass that's been mowed, that's not a good idea.