DENVER — A woman who helped her husband keep kidnapping victim Elizabeth Smart enslaved for nine months agreed Tuesday to serve 15 years in federal prison after admitting her role in the abduction.

Wanda Eileen Barzee, 64, also agreed to testify against her husband, Brian David Mitchell, whose attorneys claim he is not mentally competent to stand trial on charges relating to Smart’s kidnapping. Smart, now 22, testified last month that Mitchell snatched her from her bedroom in Salt Lake City in March 2002 and took her to a remote camp, where he held her with Barzee’s help.