Letter312:
Clarissa is naive

    Here the reader can see that Clarissa was completely naive in believing the two ladies to be genuine.  She now feels ashamed at having been so foolish.  She did not suppose that these two women could be anyone other than those they claimed to be.  They were richly dressed and played the persona of the pretended ladies so well.  She had no reason to doubt their honesty.  
    The other interesting point of this piece is that Clarissa felt the need to apologize for her dress.  The reader gets the impression that she is slightly embarrassed at being not finely dressed.  She is so concerned with her appearance even under the circumstances.  One would think that she would care little for such trivial matters at this point in her experience.