Dog running at people

I posted a question about this in the pro ecollar section but apparently missed some useful advice because a post was deleted before I read it.
My bitch, a collie cross, has recently started running towards people approaching us, barking. She runs past them then doubles back. If the person stops walking she returns to me and if they don’t she barks a bit more then returns to me. I read this as protective behaviour. She’s a rescue dog who was mistreated and has always been wary of of strangers.
What I didn’t say in the other post (forgetting that new people on forums are generally perceived to be idiots until they prove otherwise) is that since she began to do this she is on lead if we’re anywhere where we may encounter other people and is put on lead instantly if I see anyone and she’s off lead. She’s allowed off lead early in the morning in unpopulated areas so that she gets some free running every day.
I’d like to resolve this issue so that we can walk at normal times of day and around other people.

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