Yes, studying is an acceptable reason, except that it's unusual for high school students to do that. It's not like situations where people attend university abroad to save tens of thousands of dollars.
It doesn't seem like a good idea for her to stay 2-3 more years in India, while having her parents in the US and risking her green card and delaying her eligibility for citizenship, if her plan is to live in the US permanently as adult. If she attends high school in the US, she'll have more scholarship opportunities and get the experience of learning to live in the US before going off to university or a full-time job.