First I'd have your friend look at the overall sleep her daughter is getting in a 24 hour period. She and her husband may be only getting 4 hours of sleep but there is no way that the 19 year old is surviving on just that-- so maybe it's time to shorten her daytime nap(s) so she is more tired at night and ready for a good night's rest.
At night, bed time needs to be a pleasant experience and her bed needs to be a comfy/cozy/awesome place for her to want to stay in her bed. They need to make sure she has sheets and/or a blanket that she loves (either a character she loves like Disney Princesses or something else she likes like a pink blanket or a blanket with an animal on it that she likes or whatever her interests are)... Then they need to establish a bedtime ritual. It's hard to just pick one-- they sort of evolve over time, but she needs to have the expectation of "here's what will be happening to let you know it is ALMOST bedtime, and here is a routine you can look forward to every night" because toddlers need transition (as opposed to "OK, stop what you're doing, the clock says bed time") and they thrive on repeated rituals because it helps make sense of the crazy world. After bath, my toddler plays for a few minutes, then we let him know it's time for a story with his big brother (which he loves, so he happily stops playing for story time on his brother's bed)... then he goes to get his daddy for prayer time... then he goes around the house hugging everyone (which we know is his way of stalling but we allow it because it's part of his routine now!) ... then my daughter and I sing songs to him in his bed-- it's the same exact 5 verses of the itsy bitsy spider-- he tells us which verse to sing next (always in the same order) and he knows when we sing the Happy Happy spider that his sister will give him a hug and leave the room. Then I linger just for a couple of minutes and talk a little about the highlights of his day and a little about what will be happening tomorrow... then I ALWAYS say "I'll be right back". That is the KEY ingredient to keeping him laying happily in his bed. If your friend wants to try that, she needs to leave the room immediately (it helps if she says she needs to wash some dishes or put her PJs on or go potty or something else the daughter will understand is not something fun she will be missing and mom will honestly be right back). She may not believe mom at first, so it's so important that she comes back into the room in just a few minutes. She just quietly goes into the room, covers up her daughter, and says she'll be right back again. She needs to keep doing this as many times as it takes, with more and more time in between going back in to see her. I only go in once with my son now-- usually 10-15 minues after I've left-- or sometimes I just forget and he falls asleep-- depending on how tired he is.
I really do believe that if you can get your child to bed this way then they fall asleep happy and don't freak out wanting you in the middle of the night. This has worked with my own kids and I've posted it several times here before with people writing to thank me because it worked for them, too