It depends
The amount of months she is considered living with you will depend on if she changed her residency during the summer or after entering graduate school.
So if she still considered your home her permanent residence during the time she was in college only (Jan-May), she will only be considered living with you for 5 months. However, if she continued to consider your home her permanent resident during her time in college and in graduate school, then you can consider both the Jan-May (5 months) and the Sept-Dec (4 months) time periods (9 months) as her living at home.
According to the
IRS, a "qualifying child" is:
-
related to
you—your son,
daughter, stepchild, adopted child, foster child, brother, sister,
stepbrother, stepsister, or a descendant of any of them (for example, your
grandchild, niece, or nephew).
-
under age 19
(or a student under 24)—the child must be under age 19 at the end of the tax year, or
under age 24 if a full-time student for at least five months of the year,
or any age if permanently and totally disabled at any time during the
year.
-
not
self-supporting—did
not pay for over half of his or her own support during the year.
-
lives with
you—either for more
than half of the year or falls within special rules for children of parents who are
divorced, separated, or living apart (temporary absences for things like
schooling, medical treatment, vacations, business, or military service
don’t count.)
-
U.S. citizen
or resident—a
U.S. citizen, U.S. national, or resident of the United States, Canada, or
Mexico for some part of the year.
-
qualifying
child of more than one person - If they could be a qualifying child for more than one
person, you must be the person who is entitled to claim the child.
If you meet all of
these requirements, you will be able to claim her as your dependent.
