Rose is a woman enslaved by Felicity Merriman's family. Her specific age is never stated, but she has been enslaved and serving Martha Merriman specifically since before Felicity was born as stated in Felicity's New Sister. The books often refer to Rose as a "servant," despite her status as enslaved and is not a free working woman. In the notes in Felicity's Cookbook and Felicity's Cooking Studio, as well as in various "Looking Back" sections, Rose is explicitly referred to as enslaved without any ambiguity.
Rose both cooks and is a maidservant to the family. Because of her position in the household and society as enslaved, Rose does not speak back roughly to the elder Merrimans and refers to Felicity as "Miss Felicity." However, she is allowed to mildly discipline or correct the children in Mrs. Merriman's stead, such as when Felicity tried to sneak out of the house to ride Penny before the birth of Polly Merriman, and Rose reminds Felicity often that she must be responsible as the eldest child. She is knowledgeable about childbirth and babies and likely has had a hand in all four of Merriman children's births; she is explicitly shown assisting with Polly's birth (albeit indirectly as Felicity does not see the actual birth taking place). She shows skills in spinning.