Janis: The other reply was same as our situation. They call that fluid on the lungs "Pluerl Effusion" and it is a very common symptom stage 3 or 4 of Ovarian Cancer.
My wife and I found this out the hard way through 2 mis-diagnosis. Deb has reduced fluid on both lungs now after 2nd chemo with carboplatin and taxol. Make sure if your mom does chemo to use Anti nausea called Amend or Emend. It was the only one that worked for Deb and we tried about a half dozen before she could keep food down. Also if your mom gets a white blood cell booster shot after chemo make sure to premedicate with Claritin (Antihistamine)to help alleviate deep bone pain issues. I am not a doctor just telling you what worked for us after much trial and error. God Bless and Pray. At Mass this past week the Homily was to not be afraid, that God holds us in his heart. Hoping the best for your Mom. Allan