Is this harassment?(So distressed)

No, let sleeping dogs lie You can’t go to the police about something that happened a year ago if you didn’t go at the time, and as you say she hasn’t approached you for months why do you want to stir up old wounds.
Let it all die off you are over thinking and getting in a tizz Think about nice things and forget her

I don't think this could be classed as harassment. I'm not sure if you could take out a restraining order to stop her approaching either you or your mother - perhaps Citizens Advice could help?

I understand you are distressed about what this so called friend did bityoungtobegranny
I agree with Maw this really does not constitute harassment and I think your mother needs to ignore this person. For your own peace of mind its best to ignore her and not continue to let this upset your life.

But hasn't she overstepped the mark contacting my work place and still approaching us when we've told her we want nothing to do with her?

Unfortunate as this is, I don’t think it constitutes harassment and is likely to be seen as wasting police time.