It stops ok. The little screw that makes the pads move to either side doesn't work on the front canti. It's not a huge problem but if the wheel goes slightly out she'll know about it.
Do you mean the one that adds/reduces spring tension in the arms? If so, open the wire so the arms are free and move the brake arm on the side you need to add tension on away from the wheel and towards the floor.
Or use a straddle thing like this,
http://ancillary.edinburghbicycle.com/image-cache/00012606/00013612/extra-large/dia-compe-cantilever-straddle-bridge.jpg
Then just slide the straddle cable through/over it to balance the arms.