This is a very complex question. And of course, it partly depends on whether it is a functional or structural scoliosis, and whether they have fusion, and how exacerbated the curvature is. There is not one single exercise for someone with scoliosis… remember that that person is not equivalent to their scoliosis, so they need a variety of exercises, as does any other human. They do need to pay attention to their spine, to avoid compression, and to stretch and strengthen to try to create more balance. I particularly like to do one sided work, as then I can modify how much to do on each side.
I would like to recommend you read some work by Elise Browning Miller. She is a wonderful writer who has written on yoga for scoliosis for decades.
Marie, to answer your question I would need more detailed information on the degree and position of your scoliosis.
Have you tried Pilates as a workout? That maybe a good way to go, as you will learn to integrate your whole body while strengthening.
It all depends on the degree of scoliosis as Heike mentioned. And it also depends on the fitness level of your client. Some people respond very differently on exercises that others do. It’s difficult to give you a definite answer to your question because I have not assessed your client. I could say, yes it’s ok for the client to do lat pull-downs, but it won’t be the right thing to do.
I know this is not the answer you are looking for, but I would also recommend swimming for many obvious reasons. For dry land exercises and strength training, you should also consider exercises with tubing because they are not as “intense” or invasive for someone with scoliosis as any of the other strength training equipment you find in the gym. You definitely don’t want to do exercises that put stress on the spine (overhead presses, squats with barbells, ect.) I checked your profile and it shows that you have been a PT for many years now. I’m sure there are a number of exercises you can incorporate from that field into the fitness training. I hope this helps.