With your description it only means that you mother has fluid retention in extravascular (that is out side the vessels though which blood flow) space to this are added symptom of weight gain and shortness of breath
. I would consult a doctor for there are three clinical conditions which have to be excluded
1. Congestive Heart Failure. Systemic venous congestion
. No history of breathlessness, absence of any knowledge of heart disease in an educated adult and absence of aggravation of symptoms during sleep waking her up are pointers against it. Predominant right sided failure, restrictive cardiomyopathy
and constrictive pericarditis
can behave like this.
2. Renal: Nephrotic Syndrome
like condition. No problem in passing urine is there. A urine test for protein and microscopic examination of urine combined with blood tests will exclude this.
Your doctor will like to consider and exclude Hypothyroidism, Diabetes and liver disease. That should be possible with clinical examination and some simple blood tests.
There is no cause for worry but definitely cause for concern.
With best wishes
Dr Anil Grover