So sorry for your friend Yellow, she must be very worried. I don't know anything about Pierre Robin syndrome but from googling I see it is characterised by many of the palate symptoms my nephew was born with (although he never had this diagnosis).
A clef palate means that breastfeeding is not possible. He will need milk by specially adapted bottles (this could be expressed milk). DN's bottles had hard ends, not soft teats. They dribbled milk into his mouth since sucking was not possible. Ergo no dummy either.
He had an operation at 10 months to close the hole in the roof of his mouth. Until then his mouth, nose, ears and eyes were all linked directly. We got used to him sneezing milk from his eyes and nose, for example.
DN has also had issues with his hearing (wears hearing aid) and sight (wears glasses). They know him well in the Ear, Nose & Throat department at hospital.
He gets repeated ear infections. His voice is quite nasal and he has had some speech therapy to correct this. I don't know if this is related but DN also has had long term bed wetting issues (he's 9 now, still a problem).
Dr google also mentioned serious breathing issues, making sleeping a worry. This seems to be the most serious symptom your friend will face. It does suggest that the small lower jaw will 'catch up' in a year.
I realise my nephew didn't have the same syndrome as your friends child, but any information helps. My brother and sister-in-law were grateful of his clef palate diagnosis aged 10 days. Because it finally gave an explanation for his screaming (hunger - he could not feed by either breast or normal bottle, but they hadn't known this). At least your friend has her diagnosis early - so they can start coming to terms and helping their son sooner.
How can you best help her? My brother didn't like the way people recoiled from DN. I know a Mum of a downs boy who said similar, people are scared to hold the baby. Visit, ask if you may cradle the baby and coo over him like a 'normal' baby. Tell your friend something specific about how beautiful he is (he has such soft skin, gorgeous eyes etc). Tell her how lucky she is to have such an adorable baby.
Then let her cry. Ask her how she is and when she says OK say no, how are you really? At this very early stage she will have millions of questions that have no answers. Listen to her and all her worries and all her questions. If she has other children, offer to take them for a few play days so that she gets extra bonding time with the baby.
Big hugs for your friend.