Banging their head is actually a sign of self soothing, just place her down and leave her to it she will settle down and go to sleep eventually. My LB can sometimes mess around in bed for an hour or so before going to sleep as long as they are not distressed and screaming then they are fine to leave.
Just leave her to it in her cot it's how she release that last bit of build up energy before sleep. If it hurt she would cry. She will stop it soon enough. We don't talk when it's time for him to go in his cot we do our bedtime routine then kiss and say sleepy time and then it's just shhh if needed. I use to be able to pop her m in his room and leave but this sleep regression has changed that x
We are literally going through this with our almost 20 month old. We’ve found that if we ignore the behaviour he settles quicker, I used to intervene constantly (I’d be up there for an hour minimum) and we figured he actually enjoys the attention, so I sit in pure silence unless he’s really going for it and then I just say ‘lay down’ and lay him back on his pillow. Some nights he really messes around, but as the nights have gone on he’s standing and bouncing less and actually just laying down and rolling around until he falls asleep. Persevering was key for us personally with minimal interaction x