Dear Padmanarayana Krsna Prabhu ji and others,
For everyone's kind information [in case some devotees(who are supposed to know) may not be aware of it]:
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Here below is the link for Vasishtha-smriti, 5th chapter, that mentions the regulations during menses.
Regulations mentioned are:
The woman, in her course, remains impure (ashuchiH) for three nights. During that time....
(1) She should not apply collyrium (kajal in Hindi) to her eyes,
(2) should not bathe in the water,
(3) should sleep on the floor (i.e. should not use bed/furniture),
(4) should not sleep during the day time,
(5) should not touch fire (i.e. should not cook)
(6) should not make a rope,
(7) should not clean her teeth,
(8) should not eat meat,
(9) should not look at the planets such as Sun, Moon etc.,
(10) should not laugh,
(11) should not do any household work,
(12) should not drink water, out of her joined palms or out of a bell-metal, copper or iron vessel (According to Angirasa-smriti, she can either eat in her hand or use earthen vessel for eating--haste ashnIyAt mRnmaye vA).
One should not accept collyrium, ointment and food from a woman in her course.
Also, Parashara-Madhava, a commentary on Parashara-smriti by a renowned traditional scholar MAdhavAcharya (Prayashchitta-kanda, chapter 7, verse 15 and17) mentions that on the fourth day, the woman attains purity by bathing and can render service to her husband and so on even though there is no cessation of menstrual fluid (rajo-nivRtti-abhAve api bhartuH shushrUShA-Adau shuddhiH), however, as long as the menstrual fluid is not stop, the woman should not be engaged in household duties such as cooking and so on (gRha-karmaNi), (sAdhvAchArAH) or deity worship and (pitR-karma) or duties related to forefathers (nivRtte tu rajasi daivaM pitryaM cha kartavyam).
sAdhvAchArA na tAvat syAt rajo yAvat pravarttate
rajo-nivRttau gamyA strI gRha-karmaNi chaiva hi (PrAyashchitta kANDa, chapter 7, verse 17)
Translation: As long as there is no cessation of menstrual fluid, the woman should not perform sAdhu-AchAras such deity worship. Only when there is complete cessation of the menstrual fluid, can she be approached by her husband for GarbhAdhAna and can be engaged in household duties such as cooking and so on.
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There is no any specific reference that I could find in scriptures mentioning prohibition regarding not reading Spiritual books such as BG, SB etc., however, in all the traditions (Vaishnava and Smarta alike), touching scriptures or any spiritual items during periods is a taboo that is indicative of an authentic traditional practice regarding the issue. (Or else, the word "sAdhu-AchAras" might include such practices as well).
Regarding ---Whether or not, Women in their courses, can read/hear spiritual books/lectures on smart-phones or any other electronic device---IMHO scriptures or holy items in any form should be respected equally. Experienced devotees in this area can comment on it.
For more practical experience of the issue and other finer details, I request devotees to read the attached document that has been prepared by Mahaharia Prabhu with his wife, Lasika Mataji.