B2 visa renewal and green card for parents

[Nikki22]

My parents b2 visa expires in june2018
My mom had a visa extension for four months last year she visited in June 16 till feb 17 ,which was approved this was her fourth trip and first ever extension .
Her previous trips have always been shorter duration i.e. 2 months .
I m planning to file for green card as soon as I acquire my citizenship in July 2018 .
She has a valid b2 visa until June 2018 .i plan to call her in USA for a visit in march 2018 as month of may is also my graduation ceremony .
My questions are how soon can she have her visa renewed ,or reapplied as port of entry they usually stamp 6 month entry .
Saying that if she visits in march 2018 her visa would be valid just for 4 months
How can I apply for her green card in this scenario .
Thank you

[immihelp]

1. She can visit at any time during the validity of visa stamp in the passport. The actual stay will be determined by the immigration officer at the airport.
2. Once you are US citizen, you can file her green card (I-130 form). If she is in the US at that time, she can file I-485 (Adjustment of Status). If she is abroad, she can go through the consular processing to get immigrant visa.

[Nikki22]

Please clarify these doubts

1. She can visit at any time during the validity of visa stamp in the passport. The actual stay will be determined by the immigration officer at the airport.
2. Once you are US citizen, you can file her green card (I-130 form). If she is in the US at that time, she can file I-485 (Adjustment of Status). If she is abroad, she can go through the consular processing to get immigrant visa.

But as her visa is valid unill June 2018 and I become a citizen in july 2018 ..how can she stay with invalid visa
How soon can she have he visa renewed I was thinking December 2017
It would be better to have her visa done in India before she visits next time right .

Can I file for her as soon as I become a citizen ,what is the current wait peiod for adjustment of status .