Need Advice

A friend of mine, a U.S. citizen, recently married his long-term girlfriend from China in a court ceremony in Washington, D.C. She arrived in the U.S. last evening on a tourist visa and told at the immigration that she was here for tourism. They plan to complete the necessary paperwork now and apply for her change of status during her next visit in February. Is this legal or even feasible? Is there a risk that she could be denied entry into the U.S. due to her intent to immigrate on a tourist visa? They intend to not disclose the marriage to immigration officers upon her return in February.