Maintaining Permanent Residency Status for my Mother.

Hello,

My mother has been approved Green Card in July 2015; with regard to maintaining her status; I have couple of questions, Can you please help clarify?

GC received when she was outside of the United States; planning to get her in the states using valid B2 (Visitor Visa).

The questions are: 1) in order to maintain her Permanent Residency; is it required/mandatory to have her stay in the States for minimum 6months of every year?
2) Does she need to apply for Parole as she was outside of States when Permanent Residency was approved.

Due to personal reasons; thinking to get her back to the states after 6months.(before 1year of Permanent residency from data of approval).

Please advice or forward to relevant postings.

Thanks,
Kiran.