Hi Suzy,
I'm afraid that your dil would only be entitled to Contributary ESA again if she was placed into the Support Group, at a future reassessment, due to a worsening of her condition, or if she re-qualified by gaining further NI contributions from (I think it would be 2 years worth of) employment.
I don't know how long it would take DWP to respond to a change in circumstances.
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