Yes, you can legally drive a car after the airbags have deployed—but they will not re-deploy in the event of another accident.
There are some pros and cons to consider before your friend decides to keep driving her car.
Pro: Driving with deployed airbags is perfectly legal and there is no law against doing it.
Con: The airbags will not deploy for a second time if she gets into an accident.
Your friend is right to be concerned about her safety, because airbags will not re-deploy. So, she would likely suffer much worse injuries
in a second accident with no airbags then the first accident with airbags. Next steps: Your friend should replace her airbags as soon as possible and reduce her driving frequency or avoid driving altogether in the meantime. If she must drive, she should definitely avoid risky, long-distance driving.