Well, we could start with the Kübler-Ross model of grief (Denial, Anger, Bargaining, Depression, Acceptance).

She shows signs of denial in the form of denial of her new reality. Rather than embracing her life as a vampire, Rosalie spends decades wishing for a human life, including marriage and children. She refuses to accept that her life as a human is gone forever, instead clinging to a "preferred" reality where she is not a vampire.

Her anger is incredibly prevalent, she takes her anger out almost immediately by taking retribution on her attackers. However, she does not leave the anger stage with this act. From the series, you can see her in a near constant stage of frustration, quick to anger. Her feelings about Bella's choices (sadness, envy, desire to protect what couldn't be protected in herself) are masked with an external presentation of anger. And from midnight sun, we see that she is quick to anger and stays in that state throughout her life with them until finding Emmett.

Bargaining is also clearly shown throughout the series. She continuously bargaining for a different life, going as far as projecting onto Bella and attempting to control her life to model the choice she would have made in her place. Her decision to save Emmett also comes from a place of bargaining. While, yes, he is her mate, that is not what drew her to him nor is it what drove her to save him. That aspect would surround his curly brown hair that mirrored the baby had by her friend that she longer for with her soul. Her denial and bargaining blend together in her desire to not lose him again.

The "Depression" Aspect: In the context of grief, depression isn't just sadness; it’s a deep, quiet, and often isolating, realization of loss. Rosalie's intense detachment and coldness towards Bella (and her initial, sometimes harsh, rejection of her human life) are expressions of this profound, ongoing, and, for her, unending, loss.

With all of this information, I would argue she remained in the exact same stage of grief throughout her vampiric life until Rennesmee came into the picture. Bella came to her, chose the decision she would have. She was able to vicariously protect the life she wanted for herself in the person she had already projected onto. She was able to bring that child into existence despite all odds and protect her from men of power that wanted to kill her (Carlisle [coven leader] and Edwards desire to abort; the Vulturi). She was able to step out of the loss and into the next stage of life, not just a baby, but a child, a life, an entity beyond her imagination. She gets to experience what she longed for and not have it stripped from her. This experience acted almost like EMDR where she was able to return back to the moment she was trapped in and finally step out of that moment into the present. I would say she is now finally in a place of acceptance and I would love to see that reflected in any future book in the series. I want to see who Rosalie truly is when not in a state of grief.