Question

She was sitting in the train.

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Is she moving to sit down in the train?
Or she sat before and now she remains seated in the train?

Answer 1

She was sitting in the train.

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Or she sat before and she continued to remain seated in the train?

This is the effect of the past continuous tense. She sat (in the past) and remained seated (still in the past). (In the present, she is not necessarily still there!)