Just a short notice from non-expert in this field.

A young Japanese historian Hirokazu TSUJI (NB: this CB in English is not so good) has just published his dissertation about the courtesans in medieval Japan, titled as Chu sei no Yu jo: Seigyo to Mibun ('Courtesan in medieval Japan : Position and Work') (in Japanese) in 2017.
[Added 2]: Japanese summary of the book by the author himself (for award granted from the 12th Women History Award): http://nwudir.lib.nara-wu.ac.jp/dspace/bitstream/10935/4659/1/AA12781506vol2pp3-16.pdf

According to this abstract (in Japanese) of the review of his original dissertation submitted to Kyoto University in 2012, Chap. 5 and Chap. 6 seemed to deal with the separation between prostitutes and the more professiional 'Shirabjoshi' in the end of Kamakura Era, though Nanboku-Cho Era in the 14th century might be a the gap in this book between Kamakura and Sengoku periods.

 
The following is excerpts from the abstract of the thesis review, cited above:

'第五に、以上の本論文の意義・内容を支えるのは、膨大な史料の収集と解読である。鎌倉期以降の<遊女>史料は断片的であるため、鎌倉期以降のより豊かな実態の究明は遅れていた。本論文はこの点を反省し、貴族の日記・記録、歌謡史・芸能史の史料、和歌集、古文書など各種の多様な史料を、摂関期から戦国期まで文字通り博捜した。これは驚異的な作業と言える。その結果、鎌倉期以降の寺社との関わり、「遊女」集団の構造、芸能の流行との対応など、重大な事実が見えてきたのである。この中には春日若宮拝殿の「遊女」の史料群（第三章）や『正安三年業顕王西宮参詣記』（第四章）など、従来ほとんど取り上げられていない史料が含まれる。'

'(My very rough translation) The fifth strong point of this thesis is that these strong point of the dissertation are based on the vast amount of the primary sources. The courtesan study after Kamakura Period has been underdeveloped due to the fragmentary nature of the sources. In order to overcome this historiographical problem, this thesis tried to search and to collect very wide variation of the sources, [added 2]: like the diary or record of the aristocrats, songs and some sources of the arts, collection of poems (waka), and charters as well, from Regent Period to Sengoku Period. This required surprising amount of work, and as a result of this effort, the thesis shows a few new important findings, like the relationship between courtesans and the shrine/ temples after Kamakura Era, the structure of 'courtesan' group, and its correlation with the trend of arts. In these collection of the primary sources, we can find hitherto rarely known sources like Courtesan sources in Kasugawakamiya Haiden (for Chap.3) and Record of Pilgrimage of Prince Nariaki (?) to Nishinomiya in Syouan 3rd (for Chap.4)'.

 

If your friend can read Japanese, it may be interesting to her/ him.
It is also worth noting that the last section of the abstract, linked above, mention some of the previous Japanese researchers in the topic.

[Edited]: corrects the translated title as mentioned in English site of Prof. Tsuji.
[Edited 2]: adds a link to Japanese summary of the book by author; revises a translation of the excerpt of the thesis review.
[Edited 3]: corrects a link to the Japanese summary of the book by author.