she has adlib with a big bale at the moment, in the summer, we restrict her a bit and feed straw and balancer and safe and sound or happy hoof
I hadn't thought of this until @Bodshi mentioned it, but she's right. Dried forage, ie grass and haylage, has very low levels of vit E so even fed ad lib she may well be short of that unless she's getting sufficient levels from something like a balancer or well fortified hard feed fed at the recommended amount.