What is the average number of terms for a current female legislator?
female refers to gender_bio = 'F'; calculation refers to DIVIDE(COUNT(bioguide WHERE gender_bio = 'F'), COUNT(bioguide_id))
SELECT CAST(COUNT(T2.bioguide) AS REAL) / COUNT(DISTINCT T1.bioguide_id) FROM current AS T1 INNER JOIN `current-terms` AS T2 ON T1.bioguide_id = T2.bioguide WHERE T1.gender_bio = 'F'