I agree that this is a full-on money grab by Harper Lee's attorney and publisher. Rest assured that we haven't seen the last of the "Undiscovered Harper Lee" -- they are going to do everything that they possibly can to enlarge the value of her estate.
Her royalties from Mockingbird average $3M per year, and she lives a VERY simple life. The money has been piling up for years, ever since she gave up her NYC home to retire permanently to Alabama. Her elder sister Alice (an attorney who had been in practice with their father) managed her financial affairs for most of her life, Alice died last winter, still sharp at age 101. Alice successfully sued Harper Lee's former agent two years ago after it was discovered that he tricked the author into signing over the TKAM copyright to him; so that kind of flat-out deceit won't fly again. What appears to be going on now is perfectly legal, and it can be argued that it's all to Harper Lee's benefit, though the ethics of it are questionable at best.
Here's the thing, Harper Lee has absolutely no family left alive, no legal heirs, so her estate is going to take on a life of its own for quite a while. The executor of her estate is the law firm co-founded by her father, in which her present attorney is a partner, The executor is entitled to take a percentage of the value of the estate in executor's fees. Therefore, the firm has a vested interest in deliberately increasing the value of the estate as much as they can, even though their client has no need or desire for additional income.
I think it's a very ugly situation.