The Nurse has cared for Juliet since she was born, and she thinks of her as her own child. The Nurse actually lost her own child, Susan, at the time that Juliet was born, and the Nurse essentially adopted Juliet in Susan's place.
NURSE. Susan and she (God rest all Christian souls!)
Were of an age. Well, Susan is with God;
She was too good for me (1.3.22–24).
When Juliet's mother, Lady Capulet, tells Juliet that Paris wants to marry her, the Nurse is complimentary of Paris, but only superficially so. The Nurse thinks that Paris is very attractive—at least she says he is—but she doesn't have very much else to say about him.
LADY CAPULET. ...The valiant Paris seeks you for his love.
NURSE. A man, young lady! lady, such a man
As all the world—why he's a man of wax.
LADY CAPULET. Verona's summer hath not such a flower.
NURSE. Nay, he's a flower, in faith—a very flower (1.3.78–82).
The Nurse says that Paris is as physically perfect as a sculpture, or perhaps as beautiful as a flower, and that's really all she has to say about him. She says nothing about Paris's personality. All the audience needs to see is a knowing look between the Nurse and Juliet and they'll know that the Nurse is saying to Juliet that Paris is okay, but she can do better.
The Nurse knows what Juliet is looking for, or should be looking for, in a husband, and she wants the best for Juliet and for Juliet to be happy. The Nurse doesn't think that Paris is the man for her.
Compare the Nurse's faint praise of Paris—he's a "man of wax" and a "very flower"—with her description of Romeo, even though she gives her praise of Romeo in a back-handed way while she toys with Juliet's affection for him.
NURSE. Well, you have made a simple choice; you know
not how to choose a man. Romeo? No, not he. Though
his face be better than any man's, yet his leg excels all
men's; and for a hand and a foot, and a body, though
they be not to be talk'd on, yet they are past compare.
He is not the flower of courtesy, but, I'll warrant him,
as gentle as a lamb.
Your love says, like an honest gentleman, and a
courteous, and a kind, and a handsome; and, I warrant,
a virtuous...(2.5.39–45, 56–58)
The Nurse gave Paris just three lines of general, generic praise, but she gives Romeo eight lines of very specific praise, and she's still not finished praising his personality, not just his physical attributes, when she interrupts herself.
The Nurse's praise of Romeo should be enough to demonstrate that the Nurse is very much in favor of Juliet marrying Romeo. Not only that, but after the Nurse urges Juliet to go to Friar Laurence's cell to marry Romeo as soon as she can, she hurries off to find a rope ladder that Romeo can use to climb up to Juliet's bedroom later that evening after the marriage.
NURSE. Hie you to church; I must another way,
To fetch a ladder, by the which your love
Must climb a bird's nest soon when it is dark.
I am the drudge, and toil in your delight;
But you shall bear the burden soon at night (2.5.74–78).