Her parents are HER parents. They gave birth to her, gave her life, raised her, educated her, etc. No one can compare themselves to the status one’s own parents have…MIL did none of that so please dont ask for the same place as her parents.
WHy does anyone need to have a good reason? WHo does this good reason need to be given to? THe MIL? You?
No, the only advantage to living with inlaws is free babysitting. Thats it.
In the beginning, no one will be interested in joint family system. Thats life and a couple in love.
Hmmmmmmmmmm…I think this post is about your bhabi if you have one. Or a cousin bhabi if thats the case. She can be the Lady of the House…its her God given right and there is nothing you can do or say about it that will change that. It is as simple as that.
Her parents is just as deserving as your parents of care and concern. You are a female fighting for your parents and she is a female fighting for hers. VO larki kisi ke beti ha…why do inlaws forget that? As for the laws of nature…well I think you’re talking about Pakistani nature…not human nature. 
If you have someone to look after them physically, there should be no reason for any guy to hold back in helping his inlaws.
Apne parents APNE parents hote hein. Ye KHUDA ka banaya huwa rishta hai…insaan ka nahin. Thats it. No one can replace or take the place of your mother or father no matter how nice they are. If I had to choose between donating a lung (Allah na karay) to my mother or angelic MIL…it would be my mother I would choose because she gave me the life I am living today. Not my MIL. My MIL deserves utmost respect and care and concern lekin when it comes down to it, I will of course want to care for my parents before anyone else’s. THAT is a law of nature.
Bottom line: she deserves space for herself if her husband can give it to her. She also deserves to care for her parents. She also deserves to have a good relationship with her inlaws because she hasnt done anything wrong by wanting the above things.