From what I remember from my MW (I went 42+3) the risk of stillbrith is higher (but still very, very small). They can do a health check on the baby every day if your friend wishes. There is little evidence/research about what happens after 42 weeks as they don't tend to 'allow' it.
For me the risks associated with inducing were higher and more real than any risk posed by waiting. I believed in letting my body and baby decide when they were ready for birth. I did have a sweep every day from 42 weeks just to give things a gentle nudge - I thought of it as encouraging my body to birth, rather than forcing it to. I would have accepted any medical intervention if there was even the smallest sign my baby was in danger though.
Maternal age is apparently important over 40 the risk is significantly increased of so a colleague tells me. I decided not to be induced in my 2nd pregnancy and had to agree to daily scans after 10 days i only went to 11 days and then ds was born so i'm not sure how long i would have stuck it out for though i was getting so fed up. They do explain the risks in great detail so your friend must have her reasons.
FWIW my Dm went 3 weeks over with both of her babies with no ill effects.
Beyond about 42 weeks the placenta starts to slow down its manufacture of amniotic fluid and the baby receives less oxygen and nutrients as the blood flow through the placenta decreases, this is because calcium starts to deposit itself in the blood vessels supplying the placenta and they fur up like the arteries of a heavy smoker. The placenta will eventually fail altogether. Then the baby is in serious danger.
To ensure the baby isn't suffering ill effects of the gradual deterioration of the placenta post-term pregnancies are carefully monitored, daily trips to the MW or obstetrician. Also the baby can get quite large making birth more difficult and the likelihood of caesarian greater, sometimes the baby's head is literally too big to fit through the pelvis, ouch!
Some women have healthy babies after 42 weeks for every birth, it takes that long for them to grow in there, some pop out earlier, all four of my mum's were 38 weeks. Beyond 42 weeks though I would be listening carefully to what MW and doctors were saying.
I would never go that long again . My DD was stillborn at 41 weeks in October 2010 and I know part of the problem was going over my due date as the placenta was compromised. Next time I ll be going to 37 weeks and no later.I would take being induced every time over going " over" and the associated risks.