For most people, keeping the Sabbath Day (Sunday for most religions, Saturday for some) holy means that they use it as a day of worship and rest. They do not work on that day, and instead attend worship services, enjoy family time, etc.

Why don't you ask her?

They do not do any work on Sunday unless they observe Saturday as the sabbath. Some people will not go to resturants on Sunday becasue in turn they are making someone else work to cook and serve them.

For us Mormons, our Sabbath-day behavior is a reflection of the commitment we have to worship and honor our Father in Heaven. It is important to show Heavenly Father our commitment to keep our covenants. We hold the Sabbath on Sunday. The Sabbath used to be on Saturday (and is still held on Saturday by Judasism and Seventh-Day Advents). We hold it on Sunday because we find great symbolism in putting the Lord first, and we do so by having the Sabbath be on the first day of the week. The Sabbath-day consists of: 1) Every Sunday we go to the Lord's house of worship. 2) During Church, we partake of the Sacrament. The Sacrament allows us time to reflect on the Savior and His Atoning sacrifice. The Sacrament is also a time where we renew our baptismal covenants. This is key to our repentance process. When we partake in the ordinance of baptism, we enter into a covenant with God. Baptism is done by immersion...this is symbolic of being washed of our sins. As we are lowered under the water (in the same way the Savior died for us, we are buried with Him) and then being brought out of the water unto a newness of life (in the same way the Savior was resurrected...it is He who makes it possible for us to come unto a newness of life). It is important for us to remember this sacred ordinance and the covenants we made as we take the Sacrament. 3) We get to enjoy worshipping together, this allows us to uplift and strengthen each other. 4) Our faith is strengthened as we get to study the scriptures and learn more about the Gospel. 5) On this Sabbath-day, we enjoy a rest from our labors. 6) It is greatly important that we devote the entire day to growing closer to our Heavenly Father, family, friends, and fellow church members, and continue to nourish our spirits. 7) We cannot truly accomplish #6 without refraining from working (although certain needed professions hold exceptions such as surgeons, pharmacists, military, etc. as all are needed on every day of the week). 8) We are not to go to restaurants to eat, nor go shopping as we are fueling those businesses to stay open on Sunday and keeping them from their chance to be with family, and worshipping the Lord.

it means that she uses sunday as a day of worship completely devoted to the Lord. she won't do anything that isn't church related :)