You could report her to the police if she keeps it up, as a peeping tom.
Alternatively ask her if she cannot afford a television. She will be making up all sorts of stupid stories in her head about what you are up to - probably because she has nothing better to do.
Can you tell that I am also afflicted with a nosey neighbour?
Our neighbours have it in for the animals. On the other hand, they have the erroneous view that I am some sort of a grand dan martial artist, so they don't mess with me. Which just shows how ignorant they are, if they can see the state of my katas in the garden, and think I know what I am doing!
Whether it is the karate or tai chi, I have over heard the bloke who deals drugs next door telling his cronies not to mess with me, because I do Kung Fu. (I wish!)