I’m also from a Brahmin Hindu family and I feel like I need to point something out that a lot of people have failed to mention:
Hinduism is a very regional religion in India, as in that you’ll find that it’s practiced very differently in different regions and different families. Specific parts of India are more likely to follow specific gods as their kind of “patron” - as in the most prominent god in their eyes.
For example, there are people who particularly worship Kali, Ganesh or Brahma, but in my family, Krishna is the most important god that my family members worship the most.
Stories about the Gods also vary slightly depending on where you come from in India and there are hundreds of religious texts throughout the country, which partly explains the big differences between followers of the faith throughout.
A lot of Hindus, especially those of the higher castes, are vegetarian and they don’t drink alcohol in my state in particular. However, this is not always the case. Patel is a very common surname, and many people who are Patels will eat chicken or meat in general - it really depends on the family, the region and how they specifically deal with their religion.
Be careful with the surnames Khan and Singh - whilst they are very common in India, they are usually members of Islam and Sikhism respectively.
My family don’t really fast that often, but they burn incense in the house every morning and abstain from cooked or artificial foods during Navratri - Krishna’s birthday.
There isn’t really one single codified text of Hinduism like there is for Christianity, Judaism or Islam, so that explains a lot of the variation. I would argue that the Bhagvad Gita is the most prominent, but that could be because we worship Krishna in particular and that’s his book.
Yes, it is illegal to harm or kill a cow in certain parts of India, but I wouldn’t say that they’re kept like Gods. It’s more that Krishna loved them and they’re respected and revered - not quite to the same standard as a God, but definitely special treatment. They are still like vermin when you actually go to India though! They’re everywhere!
In the northern parts of India (Mumbai etc), you’ll find that most of the younger generations (below 40) only really wear sarees or other Indian outfits during special occasions. Most of the time they just wear jeans and a top. Modesty is definitely your best bet, though. The most you’ll see in India is an Indian girl with her belly showing - never legs! Longer hairstyles make more sense. Long hair is seen as a virtue on girls. Not quite as long as devout Sikhs, but at least shoulder length.
If she’s in a western country, I don’t think you need to wear a bindi either. A lot of younger Indians even in India don’t on a daily basis (especially in the north). Plus, Indians have been known to integrate very well into society!
Yes, most Hindus are Indian, but I believe that the Hare Krishna sect in particular is getting more and more popular among English people in the UK. Most are still Indian.
A good call would probably be her being part of an Indian dancing class - like Barathnatiam (I don’t know how to spell it in the English alphabet) and also wearing earrings! These should definitely be gold. It’s much more prominent in India than silver and so a lot of Indians - even western ones - stick to gold jewellery.
With regards to dyeing hair, it’s actually very common in India. In the old days, people would put mendhi in their hair to make it more brown. Now a LOT of people dye their hair to cover up greying. I think the older generations would definitely tut and sigh if your character had an audacious colour like purple, though. One of my friends has one blue streak and one purple and some of the older women really look at her weirdly.
Interesting fact: I’ve never met an Indian who can’t do eyebrow threading - myself included!
I hope this has helped. 
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