All the rules regarding non-EU licences are still defined country-by-country. The main piece of EU legislation regarding driving licences is directive 2006/126/EC and it says absolutely nothing on equivalence or recognition of non-EU licences.
In the case of France, the relevant rules are defined in Arrêté du 12 janvier 2012 fixant les conditions de reconnaissance et d'échange des permis de conduire délivrés par les Etats n'appartenant ni à l'Union européenne, ni à l'Espace économique européen.
The one-year delay runs from the moment someone becomes a resident in France, not the EU:
Tout permis de conduire délivré régulièrement au nom d'un Etat n'appartenant ni à l'Union européenne, ni à l'Espace économique européen est reconnu sur le territoire français jusqu'à l'expiration d'un délai d'un an qui suit l'acquisition de la résidence normale en France.
Another important requirement is that the licence must have been issued by the country where the holder had his or her “habitual residence” at the time the licence was issued (the goal is to make sure French residents don't go abroad to get a licence to circumvent a driving ban or another requirement of French licences). In practice, if you are a citizen of the country that issued your licence, you don't have to prove this:
Apporter la preuve de sa résidence normale […] Les ressortissants étrangers qui possèdent uniquement la nationalité de l'Etat du permis détenu ne sont pas soumis à cette condition.
(The text reads “Foreign nationals who have only the citizenship of the state that issued the permit” but if your friend shows her US passport and the licence, I doubt she will be asked anything else.)
Note that the licence must in principle be in French or accompanied by a certified French translation.