Might be worth adding some eloctrolytes, (the same as we might take if we had the same!), to her water if she gets really bad in case she gets dehydrated. You can get them from the chemist and not expensive.
I have one hen who has been runny for a year or so, yet she is otherwise active and seems healthy. I've tried all sorts and decided that's just how she is now as she's getting to be an old lady!
Judi