How long did she overstay the last time? If she overstayed more than 180 days, she is barred from re-entry for 3 years. If she overstayed less than 180 days, she could still encounter problems by CBP officers at the airport. Admission by CBP is discretionary. If she encounters difficulties, she could tell the CBP officer that she wishes to withdraw her application for admission. As for the question relating to applying for adjustment of status, she must first be admitted. If she is concerned with being admitted as a visitor, you might want to consider filing for her (if you are a US Citizen) and have her apply for her immigrant visa overseas.