The Tower reversed indicates that there are positive parts that can be drawn from your sister's new job: she will feel more secure and protected, and will have the opportunity to explore her own creative abilities. The energy of the King and Queen of Pentacles is associated with financial stability, so your sister can look forward to a good income from her new employment.
The Nine of Cups reversed represents a state of mind in which the person is too anxious, preoccupied and unable to focus on the present. This card suggests that your sister may have some anxiety-related psychological issues that could hinder her success at her job.
The Three of Cups represents a positive and encouraging achievement in the workplace. Your sister will be able to make the most of her skills and achieve her goals. The card also indicates that she may be involved in interesting projects with interesting people who will help her progress in her career.
The four cards together suggest that your sister has a good chance of success at her new job, but that she should be wary of the effects of anxiety on her productivity. The advice is to plan your goals carefully, staying focused and making sure you adopt effective strategies to manage anxiety.
In conclusion, the tarot cards indicate that your sister has a good chance of success in her new job, as long as she takes care of her moods to avoid compromising performance and final results. So the answer to the question is: Yes, your sister has a good chance of being successful at her new job.