I think this varies BIG TIME by state. I just went throught the AZ CCW class today, and if her life is not reasonably in jeapordy, you could be in trouble.
I envision him holding the strap of the purse while trying to run away. There are certain crimes that you can draw a firearm and try to stop. Robbery is one of them. But I think you had better think real hard before you show your weapon. If the BG sees your weapon on him, and he kills you, he was acting in self defense.
Especially if you could not see a weapon on him.
In Indiana you have just brandished a firearm, and may be in trouble for that.
What I would do if I were in your shoes is get a copy of your state laws. And read them and know them. If her life is not endanger, yeah she may lose her purse, and you violate a law of your state, all you have succeeded in doing is destroying your life.
Please do your research, and know your laws before you act. I legal system unfortunately does not act on honor, it just tries to maximize prosecutions, righfully or not....
Edited to say,
sorry thisisme I didn't read your post before. You give good advice!