When Juliet first meets Romeo, she actually remains more conscientious and emotionally careful than Romeo. True, she does become love-struck, as we can see from her last couple of lines in Act 1, Scene 5, "My only love, sprung from my only hate! / Too early seen unknown, and known too late" (I.v.147-148). However, she also tells Romeo that it is far too soon to make vows of affection, saying,
Although I joy in thee,
I have no joy in this contract to-night.
It is too rash, too unadvis'd, too sudden. (II.ii.122-124)
Regardless, Romeo is able to convince her to exchange vows with him, which she agrees to do so long as Romeo is truly considering marrying her. Hence, Juliet's first action that demonstrates she is allowing herself to be guided, at least in part, by her love-struck emotions is agreeing to marry Romeo, as we see in the lines, "If that thy bent of love be honourable, / Thy purpose marriage, send me word to-morrow" (II.ii.149-150).
A second action proving that Juliet is passionately love-struck over Romeo and emotional is her threat before Friar Laurence to kill herself with a dagger. Threatening to take her own life with a dagger is actually a very serious step since Juliet so far has proven herself to be very religious, and committing suicide is one of the gravest sins. The fact that Juliet is contemplating suicide proves that she is feeling deeply emotional about potentially losing Romeo and having to marry Paris. We see Juliet threaten her own life with a dagger before Friar Laurence in the lines,
If in thy wisdom thou canst give no help,
Do thou but call my resolution wise
And with this knife I'll help it presently. (V.i.53-55)
In speaking of her "resolution," Juliet is referring to taking her life with the knife she is presently holding, otherwise called a dagger. Hence we see that this action portrays Juliet as being both very emotional and very love-struck over Romeo.