I have been to Delhi, Agra, and Jaipur- among many other destinations in India. Here is something to keep in mind for Delhi- as a woman, she should avoid travelling alone. I hate to say it, but women really cannot travel alone in Delhi. The same applies to Agra and Jaipur too, but especially Delhi. There are many beautiful places to visit. The fact that she will be with her boyfriend is reassuring. My family has traveled to all these places, and we have had no bad incidents to report. Make sure she travels with a group, preferably with someone she knows.
Disclaimer I am a high school student (senior).