I have been living in Varanasi for the last two years. On one hand it is one of the most ancient cities of India depicting a wonderful history of our culture and on the other hand it is inhibited by people who are no less than animals. Girls don't feel safe walking on the roads even in morning or afternoon. Comments , eve teasing and staring until you get uncomfortable are most common here. You might also get followed by a bunch of guys (which so happened to with me several times)
Hi Prianka, generally speaking Varanasi is safe for girls. Although, I highly recommend you stay vigilant at all times. Avoid walking alone in the night. And, be wary of drinks like chai and lassi. They sometimes contain bhang and you may feel a bit hazy.
Hi while scouting the web for 'destinations for solo female travel', I saw that Varanasi like Hampi, figured in almost all the lists. It should be safe for solo female travellers, just make sure you choose a good place to stay. Happy travelling!