The best weight loss routine is called high volume routine. This is where she does exercises with little or no weights at all many times, as an example I will take legs. The best overall exercise for legs, in my opinion, is the squat. When performed properly, it works the quads, hamstrings and glutes. For it to be affective, you want to start up with about 15 reps and work your way up to 50. Then add some weight, and do it again.
Since she joined several months ago, she is most likely entitled to one free personal training session with a trainer. He/She will show your sister what to do and how to do it properly. See you PT Coordinator for details.
Good Luck,
Roman