A friend who grew up in the Russian Orthodox Church married a man from the Roman Catholic Church. They had a Catholic wedding and she now practices Roman Catholicism. She said she did not have to do anything to become Catholic. Is that correct?

No. She should speak to her pastor and request formal acceptance into full communion with the Catholic Church. There are also some protocols that are observed in receiving members from the Orthodox churches that will need some attention (see Code of Canon Law for Eastern Churches, Canons 35, and 896‐901). While she would not need to receive sacraments, her formal reception into the Catholic Church is covered by these norms and protocols, which exist to show respect for the Rite from which she came. If she wishes to practice the Latin Rite, that can be done; but there are procedures to be followed.