If you are looking for a recommendation for a completed and free-to-read novel featuring a weak princess, I would suggest reading "公主可柔弱" by 穆顏漠. This ancient romance novel tells the story of Cheng Ruoling, a princess who appears weak but is actually a highly skilled martial artist. She relies on medicine to sustain her life but is still a formidable fighter. Unfortunately, the provided search results do not specify if the novel is completed or if it can be read for free.