No, you will not include her in the household size. She would not be dependent for financial aid purposes and she is self-supporting.
@mom2collegekids, if a person in the National Guard was called to active duty for other than state or training purposes, that person is independent for aid purposes … but if he/she was not called to active duty for other than state or training purposes, they are not independent. The dependency questions do specify everything for military - that is, what counts for independent & what does not - so a student could refer to that to determine if a sibling would be considered dependent for aid purposes. Of course, in OP’s case, the sister is independent due to age & is self-supporting, so the military question is moot for her.