As a teenager, all I had for masturbation was thoughts and fantasies. I had no memories to draw upon and knew almost nothing about girls' bodies or sexuality. I had bought into the the myths of the day: 'Sugar and spice and everything nice, that's what little girls are made of.' And 'Girls only have sex to keep their boyfriends.' I did not have a sister to help educate me, either.
I was SO curious! So fascinated with what girls were like, what they thought about it, whether they had sexual thoughts and feelings like I did. I did not dare to imagine that they got horny and that some of the girls in my class might have been masturbating and having thoughts like mine. (Had I known, I would have been a more savvy teenager and probably felt more secure in my own crazy sexuality.)
I would masturbate on small details in my imagination, such as how girls would think about some aspect of sex or what words they would use. I could have a whole masturbation session just savoring the thought of whether a girl would say 'Put it in me' or 'Put it UP me.' Would she say 'PUT in in me' or 'STICK it in me'? Ohhhh, the thought of a girl saying 'I want your finger UP my CUNT.' I could beat off and come just thinking about that! And did many times! I remember hearing a girl in my class say 'screwing' and beating off that afternoon to the sound of that word in her voice. The idea that she even KNEW about penises and screwing was too much for my young teenage mind.
I know now, and can hear the reader saying, 'SO NAIVE!' I was. And in some ways I have carried those hangups all through my adult life. Fifty years later, I still love to read what females think about and what they do.