Well, Mike, the facts are thus:
You rented the house for 10 years, so there was a pre-existing condition that you knew about.
You never complained.
You purchased the house without any 'riders' regarding this 'annoying light'.
You are 'pretty sure' that this woman's Uncle was 'the original owner', and state that he 'installed the blasted thing', so it is to be presumed that you might have actually bought the house from an interest that is directly tied to your neighbor.
With all this in mind, two things ome to MY mind, regarding your complaint.
1) 'You knew the job was dangerous when you took it.' (Opening intro song to old cartoon show 'Superchicken').
2) 'Caveat Emptor' ('let the Buyer Beware').
You need to take a little personal responsibility here. You lived in the house for 10 years, and never said a word. you BOUGHT the house, and never said a word. NOW, you think you can RETROACTIVELY complain about a situation that you KNEW to exist when you bought the property.
I think that Bill Handel would state, 'You've got no case'. She got your money, and you got her house, and the situation about 'light' was well-known to you for at least a decade.
You could always try to sell, and move...