In Act I, scene iii, the Nurse reveals her own sorrows in her long, rambling monologue as she recalls Juliet as a youngster.  First, she explains how she remembers Juliet's birthday: "Come Lammas-eve at night shall she be fourteen."  From this, the reader learns that Juliet, now thirteen, is just a couple weeks from her birthday.

Next, the Nurse recalls her own daughter, Susan, who died some years before.  It is because Juliet and Susan were about the same age that the Nurse could serve as a wet nurse for Juliet.  The Nurse states:

Susan and she--God rest all Christian souls!--
Were of an age: well, Susan is with God;
She was too good for me: but, as I said,
On Lammas-eve at night shall she be fourteen.

Next, the Nurse recalls the earthquake that shook Verona on the very day she had set out to wean Juliet.  She recalls:

'Tis since the earthquake now eleven years;
And she was wean'd,--I never shall forget it,--
Of all the days of the year, upon that day:
For I had then laid wormwood to my dug....
When it did taste the wormwood on the nipple
Of my dug and felt it bitter, pretty fool,
To see it tetchy and fall out with the dug!

She next remembers how Juliet fell down and "broke her brow" that same day, and her husband helped her up:

And then my husband--God be with his soul!
A' was a merry man--took up the child:
'Yea,' quoth he, 'dost thou fall upon thy face?
Thou wilt fall backward when thou hast more wit;
Wilt thou not, Jule?'

This lets the reader/audience know that the Nurse not only lost her daughter, but her husband as well.  She has no family now other than the Capulets, no child but Juliet, which helps the audience understand why she and Juliet are so close.  The Nurse loves Juliet dearly and wants the best for her.