Wow AM! You must be good! 18 years!!!
I did it for a while when I was really young, about 12. I only got to orange belt, well, I think I did, that tournament was the last time I ever took it on.
I had this coach, I dunno where he came from, he's prolly in jail now...
and after we'd do excercises, he'd pair us up. Except he would put me with the most unmatched people he could find. Like this one girl who was an absolute nut about it, she was green belt and a few years older than me, or his other favourite was this boy also a few years older than me, he had the same dan as me but he was so much bigger and stronger. I swear if landing wasn't one of the 1st things he taught us and drilled us on, I think I may have been seriously hurt a few times.
In that last tournament I ever went to, the adjudicattor matched me with this absolute amazon and my coach just said yep, thats fine. I threw it cos I was too scared to take him on. I hid behind mum until she finally took me home.
I guess with kids, they can be serious about it and you do get the occasional little psycho girl who can take on bigger boys, but mostly I think little girls can be too easily intimidated by their opponent. At a young age its hard to remember that in Judo size does not necessarily matter.
I reckon that fun and confidence in themselves are the most important things.
Good luck AM!