Anarkali is mostly a fictional character. There are various legends and stories about her, but historical evidence to confirm her as a real person is scarce.
Most often, Anarkali is regarded as fictional. The tales about her might be embellished or created for dramatic effect rather than being based on factual events.
The story of Anarkali is a subject of debate. There's no conclusive evidence to prove it's completely true. It could be based on real events but embellished over time.
It's hard to say for sure. Some parts of the Anarkali story might be based on real events, but it's likely that there's also a lot of fiction and embellishment mixed in.
It could be from a foreign land. Maybe some traveling merchants brought it to the Hidden Leaf Village. They lost it on their journey and Naruto just happened to stumble upon it.