The Usage of Generic Article "a" Plus Singular Noun

I would like to ask the following question about seemingly generic article "a" plus singular noun as I could not find posts that sufficiently covered this topic.

I read short passages about JK Rowling:
"Many publishers, however, thought that her book had two problems. A 90,000-word book might be too long for children. In addition, boys might not read a book written by a woman. [emphasis mine]"

I think that "a 90,000-word book" and "a book written by a woman" are generic nouns, because those sentences would make general explanations, rather than about a specific book. Even if they indicate a certain unknown book which meets the condition, this non-specification suggests a kind of general tendency. I also searched for the term "a book written by a woman" and found it used probably as a generic noun notably in the feminist literature. For example, "the difference between a book written by a man and a book written by a woman is…" It is occasionally used to argue that prejudices exist against female writers’ books in general.

On the other hand, Dr. John Lawler has argued in his post (see also http://www-personal.umich.edu/~jlawler/000001.html) that "a + singular noun" is indefinite generic, which refers to the definition of a species. According to this explanation, the usage of "a + singular noun" as indefinite generic might not be applicable to the sentences I show above, because indefinite generic is too strong for these sentences, which would give general, not definitional, accounts. In addition, all the examples he showed begin with "a + singular noun" as a subject. So, I am wondering if "a + singular noun" as indefinite generic can be an object and others than a subject.

I would appreciate it if someone could let me know whether the nouns of the sentences are indefinite generic (if not definitional), and if they are not, how they should be interpreted. Also, does avoiding to use plurals, i.e. "90,000-word books" and "books written by women" have any implications? Thank you in advance.