Unreliable Narrator

I find that the relationship that the governess has with Miles, especially seen in the passages we looked at in class (pgs. 53-55) make her a poor and unreliable narrator. We can sense this romantic air about her and Miles at certain points and  the governess constantly switches her mind about Miles's character between beautiful and horrible.  How can we, as readers, trust a narrator that can't seem to make up her mind?  And let's not forget the fact that the man she is in love with she has only met twice.  This causes me to believe that there is something wrong with her mentally, or that she is just plainly not a reliable source of information.