It seems to me that the mother in "Girl" is practicing tough love. It's true that most mothers who regularly call their daughters "sluts" aren't described as "loving," but I would argue that the mother's intentions towards her daughter are good. She understands that as both a female and a West Indian, in a world filled with sexism and racism, the girl will be working against a lot of obstacles.
Most of the mother's instructions revolve around the way to do things so that the girl appears to be a perfect, proper young woman and, eventually, wife. The sheer amount of instructions and responsibilities is difficult enough. When paired with the mother's tone of annoyance and hopelessness ("is it true you sing benna in Sunday school?" and "prevent yourself from looking like the slut I know you are so bent on becoming"), it seems the girl will never live up to these expectations. The mother could be accused of overwhelming the girl, of asking her to live up to an impossible ideal, while having no confidence in her ability to do so.
Still, the mother also teaches the girl to subvert some of these excessive patriarchal expectations. She knows that men will bully her daughter, so she shows her what that looks like, as well as how a woman can bully a man. She knows that the appearance of slutty-ness is worse than the actually act of fornication, so she teaches her daughter to brew a medicine for an abortion, if she needs one. She even gives her advice on baby-making: "this is how you love a man, and if this doesn't work there are other ways, and if those don't work don't feel too bad about giving up." Even though none of these pieces of advice scream "loving mother/daughter bond," they are extremely practical for a girl trying to make her way in a restrictive society. The mother's love shows in the fact that she wants her daughter to have all the tools to succeed in the world.