Rachel is not found in the John Howland silver books. She is, however, listed in the Howland "blue books". These books are titled "John Howland of the Mayflower", by Elizabeth Pearson White (Picton Press, 1990). Rachel is in Volume 1, p 633. Her parents' bio is on p 632. This volume documents the first 5 generations of descendants of John Howland through his first child Desire Howland.
Rachel is listed as the 6th child of Lydia Fitch and Simon Glover, though the biography states that the child order is uncertain. The only information given for Rachel, beyond her name, is that she was born on Nantucket.