I would not force feed since she could choke. I would hold a small scoop or cup up to her beak and offer it often. Most chickens like wet mushy feed. If you want to try tube feeding her, there is a lot of information here:
https://www.backyardchickens.com/threads/updated-go-team-tube-feeding.805728/#post-12548717
https://www.backyardchickens.com/threads/updated-go-team-tube-feeding.805728/#post-12548717