In that case there was probably nothing you could have sold her save a Fahgettaboudit U lock or one of those square-link Abus lock-and-chain devices weighing 18 pounds which would have worked
Where and when you lock up is most of whether you get robbed, IMO. And what you lock is a lot of the rest.
A bike doesn't have to be a beater to look like just a bike---whereas anything obviously brand-new and a little flashy (giant manufacturer's logo on the down tube is a great attractant) is going to be a little bit more at risk.
it's not like most people carry a set of dikes in their pockets just ambling around .... and anyone looking for a bike can carry a set of 18" bolt cutters wrapped in a jacket and never attract attention, even as he is riding off on his (used to be someone else's) new bike.
But ... whatever. When I lived in a major city, i had three bikes stolen (one recovered.) When I moved to the sticks, I used a Really cheesy 1/4-inch cable with an in-line lock--I think it was one of the "Defeat-Me EZ" brand's products---with no trouble.
Well ... some trouble. I felt a little nervous every time I went out of the store, library, whatever .... wondering if the bike would be there.
I got a fat key-locked cable and a length of chain with a combo lock, and I now use one or the other or both, and feel much more secure. yes, someone could spend 30 minutes with nothing but a steak knife and saw through the cable and pick the combo lock (instructions are on-line ... sometimes on the sites of people who test bike locks (!!!
)) but I feel like the combo (or even one or the other) is enough of an immediate deterrent to stop a joy-rider, and the time involved would be enough to stop a certain number of thieves. I don't ever lock up near crack-town (we are so far removed from life, I wouldn't even know where it wasn't safe to lock in this town .... but I don't go there,) and anyone crack- or meth-head could easily have a set of bolt-cutters, which would defeat anything except the $200/20-pound protection.
After all, I cut the hardened steel chain for my lock---with a set of 14-inch bolt-cutters in the self-serve area of the hardware store.
Buy enough lock to buy peace of mind, and don't lock up in stupid places or at stupid times.