Hello Doctor! My Question Is, My Wife Is On 38

Hello doctor! My question is, my wife is on 38 kgs so can she take weight gainer? Or if yes so which one is best for her? I consulted with a endocrinologist he suggested some tests like t3 t4 tsh, cbc , vit d3 etc. We did it and all reports ok. So please suggest me what to do? Her weight is too low.