The house is basically like a split level with an extra story on top. The basement windows are relatively a foot above ground level and both the main and upper floor windows, which are outside, can only be reached using a ladder. There are 35 window panes and 19 screens. All are casement, double hung or picture windows and no "tricky" small windows that are difficult to clean. Almost every window has a blind on it, even including some of the doors and almost every window has some object blocking it (furniture,lamp fixture, etc).

The homeowner has lived there for almost 10 years and has never had the windows cleaned. I quoted $300 for the first clean, removing windows where possible, and then $150 for the follow up maintenance clean.

Well, I never heard back from her. Am I charging too high or too low? Is there something that I should change about how I'm going about this situation? What am I doing wrong here?

probably doing nothing wrong

I think the clue is in the fact they have not been cleaned for 10 years, this person does not want to pay anything.
Can i say i am based in the UK and our approach to window cleaning is totally different to yours, most if not all customers get cleaned once a month, albeit at low prices, but ten years??