There are a couple of factors to consider- timeframe? And body composition?
How long has the person been with the trainer? Fitness and muscle tone development takes time. I would expect some signs over a month at least with targeted exercises.
You can be relatively fit and toned with a significant layer of adipose tissue covering up that tone. Most individuals have a fantastic set of ab muscles under a heavy layer of fat.
Has she asked the trainers input and reasoning? Was improved muscle tone mentionned to the trainer as an aim prior to program setup?
There are a huge number of questions to ask on such an issue and no one set of answers.
The best advice is speak to the trainer and establish why the goal is not seemingly being achieved. If the answer is unsatisfactory consider changing trainer.
Ultimately a personal trainer is employed by the client.