Disguise

dis·guise
/disˈgīz/
1) Give (someone or oneself) a different appearance in order to conceal one's identity.
2) A means of altering one's appearance or concealing one's identity.

Meredith's entire life was just one lie after another. She wears various masks so often she can barely tell who she is anymore.
A long term theft requires her to be 'Alyssa Grayson' indefinitely. It seems like an easy thing to do.
Throw in a best friend that thinks your dead, a coworker who your tempted to kill occasionally and a boss who is intent on making her money and the job gets just a bit more complicated.