Tips for Toddler Sleep

My daughter has been in her toddler bed for about 6 weeks. She did well the first 2 weeks then we rocked her world by bringing baby brother home. For the last 3 weeks, she has been waking up 2+ times at night calling for me and crying while standing at her door (she used to sleep through the night 11-12 hours) as well as waking up for the day between 5-6am (she used to sleep until 7-730am). She has slept through the night once in the last 3 weeks & slept past 6:30am twice.. I am at a loss on what to do. How do I get her to stay in her bed in the middle of the night/put herself back to sleep without needing me to come in to tell her to get back in bed? Between a newborn and her getting up 2+ times a night I am not getting any sleep. Due to the lack of sleep her tantrums have been more frequent & on another level. I need sleep and so does she.

Does anyone have any tips or tricks to help?