Her language development could certainly be a piece of it!
I’m also wondering if she is either overtired, or oppositely has enough “sleep pressure” to fall asleep well. An “ideal schedule” at this age would be something like:
7 wake up
6:30 start bedtime
7 in bed
She needs a good 4.5-5 hours of awake time between her nap and bedtime, anything more could be causing overtiredness, anything less probably isn’t enough “sleep pressure.” It’s also important to aim for your bedtime routine to be 20-30 minutes long. Start with either a bath or at least hand, feet, and face wash, and the do teeth, jammies, stories, song, in bed. This helps her body and mind really register that sleep is coming!
Because she’s getting upset even going to her room, another suggestion would be to have some fun and really positive play time in her room during the day so it’s not just connected to the place where she protests sleep.