DD is nearly 3 1/2. She was a high needs baby who screamed a LOT and was always a dreadful sleeper till she was 2 when she suddenly started sleeping through (yay!). Since her baby brother was born in April her sleep has gone downhill again. We have waking in the night and early wakings but the main issue we have is that she now refuses to go to sleep on her own at bedtime almost every night. Our bedtime routine is rock solid, dinner, little play, bath, teeth, pjs, story, bed. She will usually let us say goodnight, turn off her light and close the door but she is now getting up within minutes and telling us she can't get to sleep. She will cry if we try and leave her to it, and this will just escalate until she's hysterical, so one of us (mainly dh) will lie on her floor or on her bed with her till she falls asleep.
What can we do/say to her to help her? We can't just leave her as she gets so upset, and it is proper sad crying not just playing us.