Final answer:
The error in the sentence is the use of the incorrect tense. The correct sentence should use the present perfect continuous tense.
Step-by-step explanation:
The error in the sentence is the use of the present continuous tense 'works' with 'since morning.' The correct sentence should use the present perfect tense to show an action that started in the past and is still relevant to the present.
The correct sentence would be: 'She has been working since morning and now she wants to take a rest.'
This sentence uses the present perfect continuous tense 'has been working' to indicate an ongoing action from the past until now.
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