Mountains are always the best for solo trips. If you are concerned about safety you can get in touch with an organiser and you can meet fellow solo travellers through them. In this manner you have the experience of solo travelling but with safety. I would suggest you have a look at https://thelandofwanderlust.com/tour-destination/yolo/. Cheers.
It completely depends on what kind of a traveller you are. You can explore places in Rajasthan if you like places rich in heritage. Eg: Pushkar, Jaisalmer, Jaipur, Udaipur. If you're fond of mountains: Jibhi, Mcleodganj, Bir in Himachal Pradesh offer amazing locations of solitude All the above locations are absolutely safe for women travellers planning to travel solo.