How to get baby to sleep through the night?

I am starting to sleep train, my 20-month-old daughter. I never had to before because she uses to sleep through the night. I do not want to let her cry it out or the Ferber method. Instead, I am going to sit in the room with her until she falls asleep. Her negative sleep association is rocking her to sleep and a sippy cup of milk. Those are my main focuses. I do not mind her needing to sleep with me in the room because we share a room for now. I was wondering if any mamas out there have done this and how long does it usually takes?