Is the neighbor a long-time resident of the street? Often people like that have some kind of sense of entitlement when it comes to newcomers - if they were behaving as though the property next door was an annex to theirs all along, then they'd probably see no problem in continuing that behavior. I had a similar problem - it's all worked itself out but my next door neighbors thought they could come onto my property any time they wanted - and bring strangers (strangers to me, that is) here to boot. It took a lot of attitude on my part to make them see that if I'm supposed to understand their (sometimes intrusive) lifestyle then they should at least make an attempt to understand mine.
Anyway, glad your aunt found her voice. And kudos for standing up for what you believed.