She's from the south. I could tell from the accent in her speech.
Literal
She [topic-は] south-region's origin is-である. That [topic-は] her speech's accent [from-から] understood [explanatory-のだが].
Two sentences. The first asserts her origin with the literary copula ~である. The second uses ~のだが ('it's that ~ but'), a soft trailing-off that invites the listener to take the inference. それは picks up 'her being from the south' as the topic. ~から marks the source of the inference.