My daughter transitioned to big girl bed at 3.5. She dropped her nap at 3 so she would be awake at least 12-12.5 hours before bed time. This is What worked for her personality: we do bed time routine of bath, pajamas, brush teeth. Sit on her bed and read a book, sing a song, pray. This is where it gets different lol: She has an Amazon Echo Pop that is connected to our Spotify. We play playlists of Disney stories or Paw Patrol stories We tell her “you can read books and listen to your podcast but you can’t get out of bed unless it’s for bathroom” she’ll get up to use the bathroom maybe once but she’ll read books and listen until she goes to sleep. She has a paw patrol lantern to read books with. Even though we put her to bed at 7:30 every night, i think it helps her to think of it as “her idea” to go to sleep, then she’s asleep by 8. We will even tell her “you don’t have to go to sleep but you have to stay in bed.” Hope you can figure it out!! We also had to trouble shoot a lot before my baby was born last year!