I agree with a lot of above although I would call this person and explain your service, DO NOT just dump, this person at least should be educted first, if I dropped all customers that did this without doing this this first I would have lost quite a few.
I would say to them, hi there I got your text message, we clean in any weather (if you clean in the rain that is) then explain that it makes no difference to the clean, also that you could clean on a nice summer day and could rain 10 mins late.
you clean all year in all weathers and you would like to prove to her why it is fine cleaning in this weather.
I would also say something on the lines of "the message we send is for you to leave access only and is not to see if they want there windows cleaned.
if there is no reason to text the customers then don't.
If she says no after you have explained the above, then replace her, but don't just dump her thats a waste of a potiential good customer a mistake IMO.
Ian