I agree with Trevor, on the subject of channels and pricing!
However, on windows such as you've described you can develope a good technique that will allow you to be much quicker, and sometimes, depending on the size of the panes, you can be quicker using a sprayer and microfibre cloth.
Don't have your applicator too wet, on multiple pane windows you can end out with a lot of mopping up to do otherwise.
Sometimes pre-detailing can work out much faster than doing the detailing after you have squeegee'd off the window, you don't have to be so fussy for one thing, and when you give the frame a wipe around, you dry off and clean the glass just the right distance in from the edges.
Either have a 'perfect fit' channel in your handle or one that is a few inches shorter than the width of the window panes, if you have a channel that is only a little shorter than the width of the pane then you can end out with kicks all over the place, you need to have the space to be able to manouver your squeegee comfortably.
As time passes of course, and you become more experienced this isn't such a problem, but even so, it still makes life easier

Hope you apologised to the customer and told her you made a c
ock up on the pricing front, and future cleans would be £xxx more!
Ian