"She does not study hard."
Translation:그녀는 열심히 공부하지 않아요.
Although this is technically correct, using the female gendered term "그녀" or "그년" is disrespectful and offensive. We usually use the neuter term "걔" instead. Using "그" is just so uncommon and a red flag of a beginner
But, to be polite, "그" can be used with more adult nouns, like "아저시" and "아가시." "아줌마," however, is also disrespectful, cuz it connotates an older woman or a married woman. But once again, avoid "녀" and "년." That connotates ❤❤❤❤❤.
From what I gather, 지 at the end of one verb stem before another verb is just a way of bridging the two together. :) If the next verb begins with 마, then yes, but if it begins with something else, 마 won't go there.
만지지 마세요. "Don't touch." Would be an example of the next verb starting with 마.
I hope that helps!