Alice Walker is the estranged wife of Simon Walker. In June 2012, Joel Dexter followed Walker where he met with Alice and their two children. After the pair left, Joel searched Alice's car and found an ID. Joel then passed on the information to Brendan Brady, who confronted Walker.
Presumably, Alice and Walker separated some point afterwards. Walker was killed in March 2013 after being pushed in front of a train by Brendan.