You avoided Section 8 but one plus about it is they can help curb the nonsense.
For example, my Section 8 tenant in one of my duplex properties claimed the 1st floor (her unit) had exclusive rights to the driveway. I told her she'd have to share it with the 2nd floor tenant.
She told me she'd have his car towed if he parked there. And so I e-mailed the Housing Authority and explained the situation and they sent her a nice letter telling her if she caused issues she could lose her voucher and be evicted.
Section 8 tenants don't want to lose their voucher.
Duplex candy lady sounds cool. If she's paying rent on time she's likely going to keep paying. Since it's a D-neighborhood I wouldn't really mind if she's taking care of the place and isn't complaining about things.
Buy some vertical blinds for the other unit. You can get them absurdly cheap online. Then tell them to keep the yard clear. If they don't, take some photos for court and then give them a 30-day notice.