This is my understanding of what Harris is saying to the Baptists: If you want someone who represents your moral values regarding abortion and homosexual marriage...I am your candidate. If you don't elect candidates like me who share your Christian values....you will have more laws protecting what you (as Baptists) consider 'sin'.
You can read the entire Harris interview here:
http://www.floridabaptistwitness.com/6298.article
Then why didn't she substitute "Christians" with "religious", "Christian ethic", "biblical foundation", etc?
No, I don't think it's necessary to parse her words or determine the meaning of "is". I think she meant exactly what she said:
If you are not electing Christians, tried and true, under public scrutiny and pressure, if you’re not electing Christians then in essence you are going to legislate sin. They can legislate sin.