My mother had my youngest brother at 46 (change of life baby). He's 16 now, everything turned out fine.
The only problem she had was with nursing. He wasn't gaining enough weight because she didn't have enough milk (hadn't even gained enough to get back to his birth weight). She was very upset about it at first- felt so guilty. The doctor told her to switch to formula because she was putting herself through too much. She wound up being so much happier and less stressed. And he was gaining weight really quickly.
If nursing is stressing her out, there is no crime in formula feeding. Millions of people turn out just fine on it. I have 4 strong, healthy, happy children who all had to be formula fed. I was only able to nurse the 1st one for 2 weeks (long story). When I went to formula, I felt like a big weight was lifted from my shoulders. Tell your friend a happy mom is more important to the baby's well-being than breast milk :)
I have 4 too- at least her youngest is already 4. Mine was not even 3 yet when my 4th was born (I'm 40 BTW) so it'll be a little easier for her. Mine were 2, 4, and 8.
Tell her not to let herself get worried about the age thing. My grandmother had my mom's youngest sibling also at 46 (her 15th child). No OB GYN, no pre-natal vitamins, no electricity or indoor plumbing. Every one of them turned out fine.
I was pretty stressed when I first found out I was expecting #4 also. I can't even imagine my life w/o her now. She's spunky and funny, and makes me laugh every day :)