Restitution of conjugal life

Yes, wife has right as per the Hindu Marriage Act for filing of such application before court. The court has to decide the application after full pleadge hearing of both the parties evidence too. so not the ground of 5 years not cohabitation not prima facie ground for defence.

so face the trial at court and court will pass appropriate order after hearing too.

She is well within her rights to seek restitution of conjugal rights even though they are living in the same house but without cohabitation.

Actually she is staying in her parental house for last 5 years or so because she was told by her in laws to leave their home. But she wants to save her marriage from divorce at any cost. Also if she is able to get RCR in her favour will it help her to prevent divorce? 

Wife can seek RCR even though she has initiated proceedings to get maintenance from her husband, it's her legal right. Granting of divorce depends  on various grounds if her husband succeeds to prove ground on which divorce is sought then order passed in RCR petition wouldn't  make any effect on granting divorce.

The decision in RCR will not be a binding decision on the divorce case.

Both are different cases, however if both are conducted jointly then the decision of one case can impact the other case.

Yes  she can file RCR petition. 

Yes, she can. However, it is meaningless indulge in court battles as a mere tactic: such tactics could evn boom rang.

Well she is very much interested to stay in her in laws house but they want to drive her away. In this case what is best legal option for her to save her relationship?