Air side transit is allowed at NRT.
Why not fly LAX NRT? It is ever so slightly shorter than LAX-CDG-NRT and reduces the risk of a misconnect, just by having one connection fewer.
If they can see that she will not make the flight at time of CDG departure, they'd probably deny her boarding to not get her stuck in Narita. If only obvious en route CDG NRT, they will probably return her to Paris.