This is a very involved question, and the answer to this question may vary immensely from person to person. Pamela writes for the reader... her letters are purposely framed to assure her parents that she remains virtuous, as well as to define and encourge virtuous behavior in the reader. As a result, we are left to wonder whether Pamela;s words are always accurate or whether they are simply the way she sees herself.
Pamela repeatedly refers to her own vanity... something that is not virtuous in itself. It is also said that she uses virtue as the means to attain her greatest desire... marriage to Mr. B., so we might also be left to wonder if her well chosen words contain various levels of hypocrisy.