What Causes Fluid In Lungs After A Heart Valve Replacement?

My sister had a valve replacement which wasn t done right, she had infection and abnormal heart rythm afterwards and had to undergo a second time, she had a new valve and the infection caused an absess on her aorta, very complicated operation and the surgeon had to scrape away some of the breast bone ? the wound was left open and drained and antibiotics given, they had to close her up after 10 days, but after a further week she has a new infection, they have operatedagain and say the infection has not gone to the bone but she is left with the wound open again and is on a vacuum drainage thing? but now they say she has fluid on her lungs, what would you say about all that. she is 66 years old and was very overweight but other than that was healthy except for only 30% use of the valve which has been replaced twice, they also say where the absess was there is now a pocket which seems to have grown? she has been hospitalized since Feb 2nd apart from the 5 days at home after the first operation. What is this fluid they areworried about and what is this pocket thing on the aorta. Seems to be getting worse instead of better.