How do I keep a safe distance from a toxic friend if encountering her regularly is unavoidable due to a shared workplace or neighborhood?

Most importantly, how do I avoid being alone with her? After seeing how she isolates and manipulates, I started to avoid one-on-one time with her. However, even when we are at a crowded public place, she tries to find an opportunity to isolate me. And I can't ask someone to be by my side all the time.

Examples:

1). I would be talking with someone else at a function. As soon as that person steps away (to get something to drink, etc.) she comes approaching me. I actually caught her staring at me when I turned my head, like she was waiting for me to become available.

2). Another time, I stepped out to go to the restroom, and I came out and saw her in the hallway (I would see this as just a coincidence if I was dealing with a healthy person).

3). When I am sitting with other people, she never asks to join and gives me an angry stare (a sign that she doesn't want to just conversate casually with me), that is unless...the people sitting around me are the ones close to me. In that case, she tries to friend-poach, which is really a form of isolation and control.