What you call pus is a brain abscess. It means germs has come from outside and spread to inside the head. Mostly they come from some kind of infection in the head area. Like an ear infection. When you have any type of leukemia your immune system doesn't work as good with fighting off infection. I assume that is how it could progress into the head.

Something taking up space increases pressure inside the skull. That causes things like headaches and nausea. More severe cases it can cause problems with speech and parts of your body being paralyzed. You can also have mental issues like being confused, slow to respond and irritated.

So yea it could have been a symptom. If it really is or if she just uses the fact I don't know. Always good doubting abusers.

How bad CLL is depends if there is a positive gene they look for which makes the illness worse than if the gene is absent. As she has lost weight and bruising shows that she needs treatment. I assume they have treated the abscess.