Is it ok to use full 2 years of Re-Entry permit duration ?

I applied for my mother's re-entry permit last year and we got the re-entry permit in January/2016. It is valid for 2 years (valid until January/2018) ? My mother left USA in Jan/2016.
I have following questions:
  1. When should i bring her back to keep her green card valid ?
  2. Will living outside India jeopardize her Medicaid eligibility after 5 years on green card ?
  3. How this impact her citizenship eligibility after 5 years on green card ?
  4. What questions will be asked at the airport on her return within 2 years ?
Thanks,
 
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