Pregnant, body swells in heat, graves disease, trace of protein in urine

My daughter is 23 weeks pregnant (second pregnancy) and she gained 100 lbs in first pregnancy mostly water weight. She has already gain 45 lbs in the pregnancy. She blows up and looks puffy. She can not take a hot shower nor can she step outside in hot humid weather. Her hands and body swell up instantly and she struggles to bend her fingers. After 1st pregnancy they diagnosed her with Graves Disease but her thyroid numbers are under control. She does have raynauds so we are well aware that autoimmune is an issue for her. No one can figure out why she swells so severe during pregnancy in the heat. She only had a trace of protein in her urine one time so preeclampsia is not yet a concern. After she swells she has horrible pains plus her skin is so tight it hurts. Any thoughts?