The trainer is probably focusing on muscle hypertophy (growth) for your friend, to change her body shape. Cardio won't change your shape (if you're a pear and only do cardio, you'll end up being a smaller pear, but a pear nonetheless). Too much cardio can be conterproductive when trying to build muscle. The P90X system has rather minimal cardio, of moderate intensity, and it's great for muscle and strength building (upper body).
It really depends on your body type (ectomorphs or hardgainers would do best on the minimal cardio/heavier weights with good recovery type of rotation, while those who tend to build muscle very easily could get away with more cardio and still build).
If your friend is currently doing "no weights," then obviously she does need to do more in that area. You say she works out 4 days a week with cardio, but don't say at what intensity or for how long. 4 days a week of a 1 1/2 hour run is different from 4 days a week of a moderate 30-45 minute workout.