Lee, who wrote To Kill a Mockingbird, is 88 years old and lives in an Alabama nursing home.
Her publisher, HarperCollins, last month announced plans to publish her second novel, titled Go Set A Watchman.
According to media releases, Ms Lee wrote the book more than 50 years ago. It features Scout as an adult, and was shelved by Ms Lee after being rejected by publishers. It was later rewritten by Ms Lee, as Mockingbird.
It was found by her lawyer, Ms Tonja Carter, last August. Ms Carter negotiated the deal to publish the book.
The announcement surprised many, since Ms Lee has been famously reluctant to release a second novel.
Debate is now raging in the US over whether somebody is taking advantage of Ms Lee, whose closest relative, her sister, Alice Lee, died last year at the age of 103.
The inquiry into her mental health was launched after friends said that Lee is not capable of consenting to the publication of the new novel.
The New York Times recently reported that Alabama public health officials visited Ms Lee, after receiving a complaint of ‘elder abuse.’
The complaint suggested Ms Lee is being manipulated, or misrepresented by those who seek to publish the book.
Ms Lee has not spoken about the book, before or since the deal was announced.
Statements attributed to her have come from Ms Carter, who now handles her day-to-day affairs.
In a statement to the Times, Michael Morrison, the president and publisher of HarperCollins, said he visited Ms. Lee over two days in February, and “she was in great spirits. It was a great meeting, and as expected, she was humorous, intelligent and gracious.”
