If this is happening at work the bouncers need to do their jobs. If there aren't any bouncers then they need to hire some. If its happening on the way home then the lady needs to consider using a taxi or getting a vehicle of her own if she is more interested in adoidance vs. confontation. Or maybe even having a friend drive her.
If she is willing to defend herself (I know it sounds to some here that to not be is foolishness) have her take a basic self defence course. Preferably an anti-rape course. Typically these classes will have a large number of female students making her feel at ease, a lot also have female instructors which will also help.
Thse classes usually teach smaller, weaker opponents (average female) devastating blows/tecniques to disable/stun stronger/larger opponents (average male) then to get outta dodge, sound advice for anyone really.
As far as improvised "weaponry"....
Steel bodied pen, fine point. Stabs to the cheek, neck, throat, bicep, groin, thigh......
Large keyring with 6" lanyard.....key flail. Try and get as colorful/decorative a lanyard as possible. Braid up colored para cord. Won't come across as a weapon and hopefully local police will see nothing askew with lashing out with her keys against a perp trying to mug/rape her.
Grab a can of good old aqua-net for the purse. Make sure she uses some of it before/during her shift. I remember gagging on the stuff when my gran came out, freshly sprayed from the bathroom as a kid. Can't imagine it being any less effective straight outta the can in the eyes/face. Make sure she uses it though, its easier to explain away when its part of her grooming habits as to why she had it with her.
Good safety whistle, blow that sucker as loud as she can as close to her assailants ears. Will deafen/hurt him, while drawing attention to herself. 2 birds with one stone.
I wish the lady the best of luck.

-Bill Liptak