Question: who is a in unmasked pretty little liars?
Answer: In the Season 3 finale "A DAngerous GAme" Jenna met with somebody in the park again and this time her face was shown and it was Shana Fring. During "'A' is for A-l-i-v-e" Mona admitted it was CeCe who visited her, although she thought it was Ali, because she was under the effect of meds.