Completed before her death...not published until 1975, but she had a hand in the writing. So, if she says that she owned the slaves and her favorite slave ran away in 1864, then I think we're going to have to believe her.
Alouette, this was FYI only.
You may well do so. Mrs. Grant dictated the memoirs, she didn't write them. They were edited by John Simon, who is credited as author instead of Mrs. Grant. And then, of course, there is the fact that the Grant family must have deliberately violated the laws of the state of Missouri, or Illinois, or the District of Columbia, or Ohio, or wherever they lived when the 13th Amendment was ratified, yet somehow this has escaped all his biographers. But hey, believe what you want.