In reply to SC:
As I said it works fine for me being slightly over twice the weight of the belayer, and works even better with a thicker rope. I'd suggest giving it a go - even if it isn't enough on its own, it might mean that a rucksack with a few rocks in strapped to her is enough to safely balance you.
At a wall, for instance, I need a 40ish kilo weight bag to balance things (typically belayer 2/3 of the climber works due to friction without an Ohm) and I was finally prompted to buy one when the new Big Rock initially only had smaller (10-15kg ish) weight bags and we needed 3, which looked silly, was really awkward and was hogging them.
Post edited at 22:46