How would you rate her physical agility?
If she has good to excellent physical agility, an ASP baton is less leathal and properly applied WILL take the wind out of someones sails.
My daughter likes steel toed boots (she's somewhat of a 'tom boy'). She aims for shins, knees and crotch.
Not so agile? Tasers, while pricey, have been turning in good results.
I'm not a pepper spray fan, as I have seen it fail to spray, leaving my girlfriend virtually defensless. Some guy tried to pull her into a cab one night and she couldn't get the spray canister to work. He saw her point it so he fled, but that was just luck.
I tried it and it only sprayed a small cloud, about 3 inches, like a breath spray.
It was my spray, and she was borrowing it, but if it failed me, I had a Sig 226 and 6 mags to back it up. For that reason, I would suggest that she might also have a back up strategy. The intended target may not be impressed with her Less Leathal Weapon.
I would also avoid a knife, as I don't want anyones bodily fluids on me that I can avoid. I nearly got into fisticuffs with a cross dresser who agressed me in a parking lot. I had my hand on some brass knuckles, intending to break the ribs under the right arm if I had to.
I called police and it ended without incident. They said he was a very good fighter and would have probably "handed me my head", or I would have certainly been hurt. 4 months later he died of Advanced AIDS. Could you imagine your wife defending herself against an adversary with bloodbourne disease with a knife? Not pretty. At least an Air Taser works from 15 feet from your target!