The host family and the au pair should exchange their contact details in advance. This will help them to get in contact during a flight delay, if anyone of them is stuck in traffic or other unavoidable situations. It’s good to talk about a meeting place to reach each other easily. The au pair should also get the phone numbers of the embassies of both countries.
The au pair should also have three sets of all the important documents like the visa, driver's licence and the passport and give one to her/his host family and leave one with her/his parents and keep the third one.
It is also very important that the au pair always carries some extra cash in case it is required to stay in a hotel or hostel or even fly back.