hi Hoping cat -
it does take a while for babies to learn the difference between night and day, and you do have bad days and good days (or nights I should say!). For example my DS2 (5 weeks) only woke once on Tuesday night, at 4.30, but last night, he woke at 1.50 and 4.20 or thereabouts. And I think he's a pretty good sleeper at night.
The best tip I had for getting the longer stretches of sleep to be at night was to try and feed the baby as much milk as you can in the day, say between 7 am and 11 pm, so that they have most of their nutrtition then and need less at night. At 3 weeks, I was waking DS2 up to feed him every 3 hours (from start of 1 feed to start of the next, so feeding at say 7, 10, 1, 4, 7 etc.). THis also means he isn't doing his longer stretches of sleep in the day time. To wake him up, I'd tickle his feet, take his legs out of his sleep suit, blow gently on his face. It is tiring, as each feed tends to take a long time at that age, often at least an hour (I am breastfeeding, don't know if this would be quicker with bottle feeding). Newborns also can't really stay awake longer than 1 1/2 hours or so, so it's pretty much feeding and sleeping at 3 weeks!
Also to do the night feeds with only a very low light, no talking or playing and in the quiet, so that the baby begins to associate those dark night time feedings as different to feeds you do during the day in the light, with noise and eye contact etc.
However, you do need to remind yourself constantly at this tiny age that a newborn can't drink enough milk to keep going for a v. long time, as their tummies are so small. It depends how big they are! Also remember there is light at the end of the tunnel - this twilight period of massive sleep deprivation every night doesn't last forever.
Wish your friend luck, and hope this is useful.