1 Nephi 5:1-9 is a fascinating glimpse at a beloved mortal woman, with all of her hopes and dreams. The Book of Mormon rarely deals with women at all, but in these verses Nephi gives a very realistic and poignant vignette of his mother's struggles with the burdens of her husband's visions.
Nephi notes that his father was "filled with joy" to see his sons return, but then notes that his mother, Sariah, was "exceedingly glad". Nephi spends more time discussing his mother's reaction, because her transition from misery to joy was so great. Nephi and his brothers had been gone long enough, and had gone on a mission she must have known to be dangerous, that she had thought them dead. Perhaps in addition to knowing Laban had the brass plates, Lehi and Sariah knew a little more about Laban, and knew that he could be dangerous, and even murderous.