I m very worried about my cat?

Our twin cats used to be house cats, they always go out together and return within an hour together, today one of our cats came home like normal and the other hasn t come home for 7 hours :( I m very worried as to where she could be, we have been out to look for her and we have tried to entice her home by shaking the treat bag. We live in the country side and there is lots of fields with long grass around that she doesn t normally go to. However even after walking through these fields we cannot find her, does anyone have any idea why she may have left for so long? We have also asked neighbors if they have seen her, however they haven t even after checking garages etc