hi
is that a 100 windows or lights? How many windows does the house have?
its 100 windows some big some small, and a few doors.
Tell her that her last window cleaner must've abandoned her because he'd REALLY underpriced. Tell her you've seen her old window cleaner still working.
Say he must've dumped you because he'd seriously underpriced the job and stayed in the areas where he's earning more.
Charge her at least £75 per month or £100 every other month. Tell her the only way to retain a good - INSURED - window cleaner is to pay him at least what he'd make cleaning 3-bedroomed semis, our bread-and-butter stuff.
Promise her that you do a good job.
If she 'dithers'; leave a card and ask her to phone you back.
I think it's great taking on work that other window cleaners have abandoned. They think that they can't get another window cleaner; so will go with your prices. Then prove that you do a good job, are regular, reliable, honest, etc and you've got a customer for at least a few years; if not for life.