There is a bit of confusion in your question in this respect. A round character can be either static or dynamic in a work of literature. A round character is a character who is well developed, but the character can either grow and change during the narrative (dynamic) or remain essentially the same (static).
Catherine Barkley has received much critical comment as one of Hemingway's fictional female characters. Critics usually view her as being a projection of male desire, a beautiful, loving woman who lives solely for her man, meeting his needs and complying with his wishes. Catherine loses herself completely in Lt. Henry; he becomes her "religion," she says. Other critics, however, find strength in Catherine even as she devotes herself to Fredric.
Since the novel is developed from Henry's first person point of view as the narrator, all we know of Catherine is what he tells us. His perceptions of her frame her character. She does not act independently from him. We know little of her personal history, except that when she meets Frederic she has suffered the loss of her fiance and feels unbalanced and emotionally vulnerable to Fredric's advances. Consequently, Catherine's character is not well developed in the novel. Her role is to complement Hemingway's protagonist and to advance the plot as Lt. Henry is developed as a Hemingway code hero during the course of the narrative. From her initial encounter with Henry until her death at the novel's conclusion, Catherine remains essentially a static character. Despite all that happens to her along the way, she remains essentially the same woman, Fredrick Henry's (and perhaps Hemingway's) romantic ideal.