Question Summary:
My sister is being very annoying and disrespectful; how may I change her?

Question Detail:

AOA, my elder sister's behaviour has dramatically changed since I have got married. She has become more aggressive & has no regard for her parents, elders or anyone. She is always blaming others & never accepts her own fault. Every week a heated argument takes place in the home because of her & she is very against my wife even though most of the times it's not her fault.
My wife is very religious & MasAllah she has changed me as well for my betterment as I personally believe that I am becoming a better Muslim since I have got married but my elder sister is always attacking her & is making her & everyone's life miserable.
I want to live with my parents & family because I want to look after them as my elder sister is not capable of looking after them as she is always arguing with my parents & have no respect for them either
She reads occasional prayers & Holy Quran but is not a strict Muslim. If we talk to her about religion she doesn't listen but in fact makes the whole situation worse.
There is no point talking to her as we all have given up on her.
Can you please advise that what we should do in this situation as my parents are not in a state to bear all this?
Kindly advice us of any Duas/Surah's which we can read to make everything better.

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
Your sister’s aggressive attitude is indeed a matter of concern. In addressing such issues, the correct diagnosis of the problem is important to determine the cause of the problem. We are not aware of much information concerning your sister and are unable to determine the actual cause of her aggressive attitude. You refer to your marriage. Is it possible that your wife is a threat to her? What is your sister’s age? Is she of marriageable age? If so, why is she yet not married? All these issues have to be explained for proper diagnosis of the problem. Offering advices without understanding the cause of the problem is tantamount to offering medicine without being aware of the actual sickness itself. Search for the answers of such questions and related queries and try to determine the root cause of the problem. The solution thereafter will be quite easy. 
In the meanwhile, increase your ibaadah and illuminate the spiritual environment of the house. Such an environment will have an effect on her. She will realize her mistakes and feel she is not doing the right thing.
Apart from the above-mentioned, it would also be beneficial for you and your family to identify such a woman that is religious and willing to help. Such a woman may befriend you sister and guide her to change her attitude and conduct. We also advise you to turn towards and beseech the guidance and help of Allah. Allah Ta’ala is the ultimate controller of the hearts.
And Allah Ta’āla Knows Best
AbdulMannan Nizami
Student Darul Iftaa
Chicago, IL, USA
Checked and Approved by,
Mufti Ebrahim Desai.
www.daruliftaa.net