Seymour may be best known for her popular CBS series "Dr. Quinn, Medicine Woman," which went off the air in 1998.
"I hadn't actually gone out and done any acting in a year and a half, so I though it'd be fun to get back in the saddle again, as it were, but to do something completely different from 'Dr. Quinn' and completely different from what people are used to seeing me do," said Seymour at Tuesday's Zap2it.com.
In the "Law & Order" episode Seymour plays a wealthy socialite whose family is torn apart by a rape and murder.
Seymour, since "Dr. Quinn, has spent her time showing her paintings around the country, raising a family, creating home furnishings for Saks Inc., developing behind-the-camera projects with husband James Keach, and designing women's and children's clothing lines, with just a little television work.
In the coming months, she plans to star in a Court TV movie and will work in a production capacity on director James Mangold's upcoming Johnny Cash biographical movie.