Question Summary:
Does my Shahada need to be official? Can I involve Hindu rituals in my marriage? Do I have to slaughter and eat meat?

Question Detail:

Recently one of my friend informed me that we should avoid drinking Tang (powder). It is to be noted that I stay in Bangladesh and the Tang product that I have bought is a product of Bahrain. Is the Tang drink (powder) really haram? 

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
If the girl in reference proclaims the Shahada while understanding and believing in the concept of Shahada, then she is a Muslim.[1] There is no need to officiate her Shahada. If she informs people that she is a Muslim, then that is sufficient. Muslims could inform others about her Islam. 
As a Muslim, she cannot marry a non-Muslim[2] or practice on Hindu marriage rituals which constitute practices of Kufr.[3] You did not specify what she refers to “walking around” as a Hindu marriage ritual. If it refers to the “Saath Phere”, then that constitutes Kufr and Shirk which is not permissible even though the intention may be to merely satisfy the parents.[4]
A Muslim can be a vegetarian. It is a personal lifestyle choice. It is not necessary to eat meat. The slaughter of an animal during the days of Eid Al-Adha (11^th, 12^th, and 13^th of Zhul Hijjah) is only on those who are financially able and have the Nisab of Zakat.[5]
 
 
 
And Allah Ta’āla Knows Best
Abdullah ibn Mohammed Aijaz
Student Darul Iftaa
Baltimore, USA
Checked and Approved by,
Mufti Ebrahim Desai