After two months of being in hosp my mom was finally moved to a rehab. After a week on being there her legs r swelling up again. Could her pulmonary hypertension be further along than we think?

May be. Sometimes in rehab, they are not as aggressive with diuretics. The swelling may be a sign that the phtn is worse, but it may be as simple as her diet been high on salt or increase fluid intake. I would ask the doctor to address the fluid retention...
PHTN. Pulmonary hypertension can "strain" the right heart leading to edema which is frequently treated with diuretics. An echocardiogram will show how high pulmonary pressures are & how right heart is performing.