Hello Welshthistle,
I am not that experienced however, as I understand it, broody hens stop laying and can put other hens in the flock off laying. She may well start plucking out her own chest feathers as this helps to keep the eggs warm
Your options are:
1 Trying anti-broody measures (you can type broody hen in the search box in the top right hand corner and you will find plenty of info and suggestions)
broody cage with wire mesh on the bottom so her underneath feels cold
sitting hen in cold water
keep lifting her off the nest
(these are only some of the suggestions)
2 Let her sit on fertile eggs and hatch them
Someone with more experience will be along to give advice. In the meantime Good Luck!