Hello and welcome to MedHelp's forums. We are really sorry to hear about your mother. That sounds very stressful and worrying and we are sorry your family is going through this. The best source of information is obviously her doctors and it helps to write down all of your questions and concerns and attend the next appointment with her. Writing it down ahead of time assures you don't forget or get side tracked and can get the information you need. This is good practice when serious conditions are being treated.
Most necrotizing granulomas can be caused by either fungal infections or micobacteria (TB being one but there are others), however, it is also very often unclear as to the cause. Basically it is often a group of cells that form when the body is trying to fight off an infection and they stay. This is why TB is often associated with it but I do not that this is not the case with your mother.
Here is a pretty comprehensive list of conditions that can cause necrotizing granulomas. https://emedicine.medscape.com/article/2078678-overview.
When is your follow up with your mother's doctor? What is your next step?
Could you elaborate on increased cavity in lung?
How is your mother doing?