Then the heroine went on a journey. By train.
Guess that settles that. A 19th-century-ish setting. Because certain other plot element prevent a 20th century one.
There's a lot more to be settled, but at least the technology level is set.
Unless, of course, plot elements come up that require that be revised out, or at least the setting be a mish-mash of eras fused together.