Old girl (6)
I believe the answer is:
alumna
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">old girl</span>' is the definition.<br/ ><span class="explanation-format__explanation">(female graduate of a school or college)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for alumna that I've seen before include "She studied" , "Harvard graduate" , "Female graduate" , "Female former pupil" , "Manual (anag) - old girl" .)