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Change Shape (Su) A creature with this special quality has the ability to assume the appearance of a specific creature or type of creature (usually a humanoid), but retains most of its own physical qualities. ... This ability functions as a polymorph spell, the type of which is listed in the creature's description, but the creature does not adjust its ability scores (although it gains any other abilities of the creature it mimics). Unless otherwise stated, it can remain in an alternate form indefinitely.
Polymorph: Unless otherwise noted, polymorph spells cannot be used to change into specific individuals. Although many of the fine details can be controlled, your appearance is always that of a generic member of that creature's type. Polymorph spells cannot be used to assume the form of a creature with a template or an advanced version of a creature.
I am looking at a Succubus with the Change Shape (Alter Self) ability. She wants to disguise herself as a human, so she uses Change Shape to become a Human female who goes by the name of Gail. She reverts to her natural form to fly somewhere.
Can she change into "Gail"'s form again?
She is not changing to look like a specific real Human. She just wants the same form she took before, but the rules state it is always generic.