As part of my profession, you are taught that all accidents are preventable, if you identify the root cause. Corporate safety culture, poor training or competency and many other factors besides human error.
She should have had a torch, and known when to use it (obv!) the area should have been well lit, and the kerbs maintained. At best it's contributory negligence*
*I've not seen the kerb to see if it was in a state of disrepair, if so, then that in itself is a failing under HASAWA (provide suitable access and egress) and falls on the petrol station owner / whoever is responsible for their up keeping.
As you rightly point out, however, it might not be reasonably practicable to remove every possible hazard, but you have to justify your position to the local authority / HSE should you end up in court. E.g it would be hard to argue a broken kerb if the cost is only a few hundred pounds.
What I do find ironic is that police officers are now free of prosecution under the HASAWA while performing their duties, yet, it clearly doesn't stop stupid bints claiming after falling over. I detest the claim culture we're in