Pretty sure it applies to her without regard to her willingness, IF she crossed state lines:
https://www.law.cornell.edu/uscode/text/18/1201
U.S. Code Title 18 Part I Chapter 55 § 1201
18 U.S. Code § 1201 - Kidnapping
...
(g) Special Rule for Certain Offenses Involving Children.
(1)To whom applicable.If
(A) the victim of an offense under this section has not attained the age of eighteen years; and
(B) the offender
(i) has attained such age; and
(ii) is not
(I) a parent;
(II) a grandparent;
(III) a brother;
(IV) a sister;
(V) an aunt;
(VI) an uncle; or
(VII) an individual having legal custody of the victim;
It would appear it is a federal crime yes as written what you said