Are you in Canton Geneva or Canton Vaud.  Bringing someone non-EU into Vaud is next to impossible. 

There's a list of au pair agencies in the knowitall passport book.

www.knowitall.ch

If you Paul are African your self, this au pair you have found is from the same country you or your mother or father or your wife and her family then yes you can get this au pair to work for you and she will get au pair permit. Or you are swiss then again it is possible but if she is not from your home country and you are holding permit your self in here, forget the au pair and find someone who is from EU or all ready have permit.

Hi Paul, 

I currently work as an au pair and am not an EU citizen. I talked to my employer and they used the agency Compagna with all of their au pairs (http://www.compagna-aupair.ch/). I recommend you contact this agency and ask them about your idea. She says they are well connected within the permit office in a sense that they know all the laws and rules. 

That being said, it is extremely unlikely that you will be successful in getting her here as an au pair if she is from an African country. You could try hiring her as a Nanny (a different type of permit) but that will be tough too. The only other option I can think of that hasn't been mentioned above is if you have any sort of diplomatic status? That changes the game and greatly improves your odds of getting her here. 

Good luck!