There is very little information about this woman, so I apologize for the short article. I was amazed to find that the Japanese Wiki Corpus had an article on her, so most of the information will be coming from that source.
Yamanote-dono (?—July 20, 1613) was the wife to Sanada Masayuki and the mother to Sanada Nobuyuki and Sanada Yukimura. Much like other women from this era, little is known about her life, especially her childhood. Yet, there is one interesting thing. Many sources state that Yamanote-dono is the sister to Ishida Mitsunari.(1) Others, including the Japanese Wiki Corpus, suggest that she is the daughter of Uda Yoritada. Going even further, one source states that she not only the eldest daughter to Uda Yoritada, but her younger sister is also Kōgetsu-in, the wife to Ishida Mitsunari.(2) It is not clear in the sources that claim that she is the sister to Mitsunari if they are referring to her as an in-law or not, so at least for now, her familial ties are up for debate.
Yamanote-dono married Sanada Masayuki in 1564, but little is known about her aside from her children. She was staying at Ōsaka prior to the Battle at Sekigahara and was one of the few who managed to escape before trouble broke out. Masayuki and Yukimura fought for the Western Army and as a result, were sent into exile at Kudoyama in Kii Province early in 1601. While Yukimura brought his family with him into exile, Yamanote-dono was sent to Ueda Castle and placed in the care of Sanada Nobuyuki. She would later become a priestess at Dairin-ji and changed her name to Kanshoin.
The last mention she gets in history is her death. She committed suicide on the second anniversary of Masayuki’s death, who passed in July 1611. She is buried in Dairin-ji in Nagano Prefecture.
Sources
Main source: “Yamanote-dono”, Japanese Wiki Corpus. https://www.japanese-wiki-corpus.org/person/Yamanote%20Dono.html, last accessed 7/9/2022
- Glenn, Chris. The Battle of Sekigahara: The Greatest, Bloodiest, Most Decisive Samurai Battle Ever (2021), p. 42
- “Uda Yoritada”, SengokuJidai.org. Uda Yoritada「宇多頼忠」 | Sengoku Jidai, last accessed 7/9/2022