Hi Priscilla
Yes, all babies have differing amounts of sleep that they require.
However, the amount of sleep that your friend's baby is getting is very little. I notice that you mention that the baby sleeps fine in the car - it sounds like the baby needs help learning how to fall asleep independently - babies are not "born" with that ability, they have to be taught. That means learning how to fall asleep in their cot, not being rocked or walked or driven or fed to sleep.
I think that you might help your friend by explaining that the baby needs to be taught to sleep, and that they might do that by starting to put the baby into the cot very drowsy but still awake. They can use pat/shh to help the baby settle. As that becomes more successful, they can start to put the baby into bed slightly more awake and so on. It will be a long process because the baby has not been taught to sleep yet, so your friend will need to be very patient. She must remember that she has taught the baby to fall asleep in the car and that the baby now needs to be taught a new way.
As the baby learns to fall asleep independently, he should be able to sleep longer stretches because he can transition himself into the next sleep cycle.
The other thing that your friend should look at is making sure that the baby is on a reasonable feeding "routine" during the day. By that I mean the baby should be eating at approximately 4 hourly intervals. After their feed the baby should have some play time, followed by a nap. I think with an older child as well, naps might be difficult to do sleep training - she should try where she can but mainly just try to ensure that the baby gets some sleep, and focus her sleep training for the beginning of the night.
She has a lot of work to do - but those are probably the most logical places to start. Good luck to you both.
Jo