The important thing is to care for the victim - not play cops and robbers.
Would your friend have been happy to see you or your dog knifed in a pursuit? I doubt that someone who has just attacked an old lady is going to meekly submit to a challenge.
If your friend feels so strongly, suggest she joins the volunteer Police force.

Probably not willingly let Sadie go, but Bruce was a hero a few years back when an old lady suffered the same here and was badly hurt, Bruce gave chase without any intervention from me, and they caught him just round the corner....with a big huge thank you for a Border Collie......namely Bruce. I have to say once it was all over I was very proud and he got a huge box of treats from the family and a BIG thank you from police.

But its not something I would deliberately '''send''' him in to

However an untrained BC is not likely to inflict the sort of injuries a bite trained GSD would...............

I realise that Im not thick.......

Which is why I said I agreed about NOT letting Sadie.

And All dogs bite and can inflict injuries