She wants the ‘discoloration’ taken off, but I’m not sure a standard HW mix will do the trick, especially on older painted wood siding. Not too keen on walking the roof pitch either, bad enough when dry for WC but running a hose and spraying would slicken it up quite a bit.
I would give it a try. You just never know. No need to walk that roof. If anything just shoot it from the gutter line off a ladder. I wouldn’t be surprised if a normal house wash took care of that. Just set expectations up front.
I always turn down work that is paint prep work. Mainly because a painter will want it done his way. If you don’t do it right he will tell the customer “I have to redo his work to do mine” and they feel ripped off.