I would not consider the risk of falling especially high on those stairs, just because they aren’t to current regs doesn’t instantly make them dangerous. If I was doing a risk assessment on them I may note for improvement at some point but not urgently though I’d probably highlight the treads for the visually impaired.
I think there is a tendency to forget that everyone has a personal duty of care, sorry for the op’s other half but if she’d been a bit more careful the accident may well not have happened.