One thing that we must remember when analyzing the thoughts and actions of Juliet is that she was very, very young. In fact, we know that she is only thirteen, because her father says so to Paris. Lord Capulet says to Paris,
She hath not seen the change of fourteen years;
Let two more summers wither in their pride
Ere we may think her ripe to be a bride. (I.ii.9-11)
Being only thirteen has a significant impact on what Juliet does and thinks. Hence, one can see that if one truly was Juliet and just as youthful and naive, one would certainly succumb to the wiser, older counsel of Friar Laurence, especially since one considers him to be a spiritual adviser. If one truly was Juliet, sadly, one would have made the same foolish mistake that she made, and one would have followed through with Friar Laurence's plan to fake his/her death.
However, if one were older and wiser than Juliet, one would have been able to quickly see that adding deception on top of deception only creates more problems. Both Juliet and Friar Laurence have already deceived Juliet's parents by, at least, not letting them know about the marriage. While it was legal for a woman to marry at the age of thirteen without parental consent, not having at least parental acknowledgement certainly caused further problems ("Civil Marriage," Catholic Enyclopedia). If one was older and wiser than Juliet, one would have seen that an alternative course would have been for Friar Laurence to go to Juliet's father and explain why a marriage to Paris would be legally and spiritually impossible. Juliet would probably have been disinherited by her father, as we see him threaten to do in the lines,
[H]ang, beg, starve, die in the streets,
For, by my soul, I'll ne'er acknowledge thee,
Nor what is mine shall never do thee good. (III.v.201-203)
In saying, "Nor what is mine shall never thee good," Lord Capulet is threatening to disinherit her. Hence, even though acknowledging her marriage to Romeo would have resulted in being disinherited, she would have been free to travel on to Mantua and live happily ever after in exile, which is what she was planning to do anyway.
Hence, an older and wiser person can easily see that being honest instead of being deceptive would have been the best course of action, and would have preserved both Juliet's and Romeo's lives.