(covers information from several alternate timelines)
Wallace was the maiden name of the wife of Alexander Marcus. She was the mother of Carol Marcus and the grandmother of David Marcus. (Star Trek II: The Wrath of Khan)
In 2259 of the alternate reality, Carol Marcus used the alias "Carol Wallace", combining her own first name with her mother's maiden name, to board the USS Enterprise, so that no one would associate her with her father, Alexander Marcus. Spock later confronted Carol with the truth of her deception in the Enterprise's weapons bay. (Star Trek Into Darkness)
This character was only mentioned in dialogue.
A deleted scene would have established her as having lived in England, where she raised Carol Marcus, thus explaining Carol's English accent. [1]
The Star Trek app for smartphones and tablets revealed her first name to be "June (β)".