Your lady needs veg nutes atleast until she starts to stretch. Than u can go to a well balanced transition feed. Start using bud ignitor ect if ur going that route. Bit still than make sure it's even balanced. There is still a large demand for nitrogen when shes stretching and throwing off rampant growth preparing for full bloom. Happy growing and stay lit fam.
I think you're a bit behind in growth and timing. In theory, they start to flower on their own in about 3, 4, or 5 weeks at most. Wait another week and you'll see how it starts to show signs of pre-flower. Cheers!