thanx for coming to HCM
Your mother has got small cell lung cancer
stage4/extensive disease. definitely chemo has got its life prolonging role and palliative effect. since Brain has been involed you need to go for palliative cranial irradiation which has got 5% benefit and is recommended.
low sodium level can be due to a syndrome called SIADH (sybdrome of inappropriate antidiuretic hormone) which tends to decrease the sodium level. If it is rising then ok.
since she has cancer and she is diabetic there is increase chances of infection so sugar control should be optimum.
will further deteriorate the lung function so please help her to quit it via nicotine
gums, patches etc.