How many research assistants does the female professor with the lowest teaching ability have?
research assistant refers to the student who serves for research where the abbreviation is RA; professor with the lowest teaching ability refers to prof_id where teachability = '1';
SELECT COUNT(T1.student_id) FROM RA AS T1 INNER JOIN prof AS T2 ON T1.prof_id = T2.prof_id WHERE T2.teachingability = '1' AND T2.gender = 'Female'