I can understand how a male could use a roll on catheter, but what is there for the females?
I'm not in a position to take female friends / girlfriend(s) on any long distance X-countries so I've never worried about it.
But in case you have to:
From a well respected Woman's Gliding Champion personal website:
http://www.freeflight.org.uk/plumbing/
or the bottom of the page:
DG Flugzeugbau: To Pee Or Not To Pee