Like title says, I am moving to a city where I onced dated someone with BPD. It didn't end well for many of the obvious reasons and we haven't spoken or seen each other in several years.  I'd like to keep it that way. 

I am hoping to get some advice from all of you about the kindest, best way to handle things if I randomly bump into her. I really do wish her all the best, but I have no interest in being her friend.

If we do get talking (example--she walks up to me and says hi) what is the best way to handle this?

What are some things I should avoid saying or doing to keep a boundary firm in the event we somehow meet? I absolutely do not want to be friends.