If she's planning to breastfeed, she'll have to give up her job for a while regardless. Newborns need to be fed on demand, and they tend to eat every 2 hours. Some of them even cluster feed, and will eat every hour.

As someone who currently has a baby, I have to admit, I wouldn't be willing to leave my newborn with someone who doesn't have the proper credentials. I'd want them to know first aid for babies, to know what to do if the baby is choking, to know what to do when the baby is going through the period of purple crying or colic (even parents have been known to get frustrated and have to put the baby down and walk away, after all), etc.

Taking care of a newborn isn't easy. The newborn period is probably the hardest of any of the baby stages. Some of them spend most of their time crying, they need to eat every 2-3 hours, they have no concept of sleep schedules, etc.

Definitely talk with her first. She may appreciate you being willing to babysit, at the very least. When I had a newborn, I would have been so grateful if someone had offered to at least babysit. I would have turned down an offer to nanny, but an offer to babysit? Heck yes.