Strictly speaking, the choice of the child's name is not Tan-Tan's decision but the author's.
The book's setting is a Caribbean-colonised planet (Toussaint) and another planet, New Half-Way Tree, to which criminals get exiled.
The book references many elements of Caribbean culture, including its carnival tradition (hence the title's Robber Queen) and folklore.
It does not explicitly reference the history of slavery in the USA.
People raised in the USA will very likely recognise the reference to Harriet Tubman. (The name was new to me.) Harriet Tubman was born into slavery around 1822 and grew up on a plantation in Maryland where she was badly beaten.
In 1849 her master Edward Brodess died and his widow began to sell his slaves. In the process, their families were broken up.
On Monday 17 September 1849 Harriet (then still known as Minty) and her brothers decided to escape.
However, her brothers became frightened and soon returned to the plantation; Harriett went back with them.
In October she escaped again, and she would later work for the abolitionist John Brown.
(See "17 September 1849: Harriet Tubman makes a bid for freedom", BBC History Magazine, September 2018, p. 8.)
This is why the book's "other narrator", whose words are printed in a different font, adds, "Tubman: the human bridge from slavery to freedom."
There are also a few similarities between Tan-Tan and Harriet Tubman. Edward Brodess' widow published an advertisement with a reward for people who would bring back Minty/Harriet and her brothers.
Similarly, for much of the book, Tan-Tan is hunted by her father's widow Janisette.
In addition, Harriet Tubman undertook several missions to rescue other slaves. Her name is strongly associated with the Underground Railroad; there is a biography by Charlotte Taylor and Stephen Feinstein that calls her Hero of the Underground Railroad and another one by Anne Schraff that calls here the Moses of the Underground Railroad. Tan-Tan takes on the role of "Robber Queen" who helps people who are being cheater or oppressed. (Midnight Robber is not a retelling of Harriet Tubman's story, though.)