I feel helpless

I don’t get to sleep until 4-5 in the morning...I had my son November 23, he’s breastfeeding and cluster feeds at night, and my daughter is 1 she’ll be 2 in 3 months. She’s been having nightmares and she’ll be screaming bloody murder and when I check on her her eyes are still closed while she’s screaming.... what can I do to help her. She has some light in her room from the tv (she’s never slept without the noise of a tv in the background) and I plan on getting her a night light when I go to the store later to put by her bed. Is there anything else I could do to help or anything that could be causing nightmares. Any thing that could help me figure out how to help her is appreciated. TIA.