I can fully understand your neighbours point of view but......
Your land, your drive, your property and it's up to you what you do with it. If you want to put gates up, I can't see how anyone can stop you. If I were you,
I would just fit them. Not to be malicious, just because that's what I wanted to do.
You could actually build a single story extension, right up to her wall and no-one could do anything about it. At the end of the day, the window issue is with her property (and new owners issue) and not yours.
It's not ideal for your neighbours but the fault lies with whoever designed/built the houses. Seeing as they can't even access the windows to clean or maintain them, it suggests your house was designed/built after theirs? Surely nobody would knowingly design it like that?