My mother has congestive heart failure with kidney failure and fluid build up in her lungs. been in hospital on & off for 3 months. death soon?

Depends,: The details that matter include how bad are kidneys eg stage 3, 4, 5? And how bad is heart ejection fraction ef, how low? 30, 20, 10? How responsive is she to water pills? Does she have other illnesses (comorbidities)? She sounds certainly very ill. Ask her doc about more information including above questions and the discussion will flow more naturally to better answer the question of longevity.

Mother's prognosis: Your best source of information about your mother's condition is from her physicians (p), as they know her clinical status best of you. You did not provide any information about her lab work or whether she is on dialysis for her kidney failure. Speak to her p's as they know her best of all and can answer your questions in a meaningful manner.