Whether foot sauna can cure my mom's rheumatism?

Hi, I came here for some professional advice. My mom's got a rheumatism and her arthrosis hurts when weather changes. Our doctor suggest her to try foot sauna so we are looking to buy her a portable one. But as I look through online I found little reliable recommendation on it. (call me sceptic...) As the healingwell seems safe and reliable on diseases, so, would you please tell me what's the effects of those foot saunas selling online? and what kind of feature it should have to help to cure rheumatism?