Janie's grandmother, Nanny, was born into slavery. That did much to shape her outlook on life. While a slave, she was the lover of her white master. She became pregnant and gave birth to a mixed race child (Leafy). Leafy also gave birth to a white man's child (Janie), but Leafy was raped and left after giving birth. That means Nanny was Janie's main care giver. Nanny's main goal for Janie is that she marries a legitimate husband, so she doesn't fall into the emerging family cycle.
That's not a bad desire, but Nanny's version of a legitimate husband for Janie is a bit off. Janie wants to marry for love, but Nanny thinks that is pointless. She pushes Janie to marry for freedom and security, and because of her time as a slave she believes that freedom and security equals wealth and idleness. Nanny forces Janie to marry a wealthy land owner.
It's hard to fault Nanny for wanting her granddaughter to have a life of wealth and respectability. Nanny never had it, but cares deeply that Janie will. That makes Nanny focused on Janie. Again, that's not a bad thing initially. Nanny is caring. Nanny is focused. Nanny is determined (perhaps stubborn is a better word). She loves Janie. All of those things are obvious. The frustrating part about Nanny though is that she doesn't consider what Janie wants. She never treats Janie like an independent woman, which makes Nanny and incredibly controlling person. It's sad that she dies before any kind of reconciliation can occur between Janie and Nanny.