My husband and I finally went with http://www.CoastalSaunas.com
and have been very happy, but there are a lot out there now. Funny, it was easier for me to buy my car.
You might want to let your sister know, she will not find an infrared sauna that heats up to 190 degrees. Infrared works differently than the traditional saunas with the hot rocks. Since it heats your core instead of the air, you will sweat at a much lower temperature than the traditional type saunas. In turn you can stay in the sauna longer and get many more benefits. The most I've seen go to 150, but since your core is being heated, many sweat at 110.
If you have any more questions let me know. I have a wellness center with 3 of them running all day.