It's isn't just the UTI, or the pain that the patient may be
experiencing in a way that uses up all the mental capacity left.

If the brain is deteriorating, all of the bodily functions that
depend on autonomous brain functions (like keeping the heart
beating, breathing, digestive tract contractions to move food and
waste through the bowels, etc.) can be affected.  

It becomes more noticeable when the patient begins to have
trouble swallowing, or starts losing his or her balance
frequently.  Usually they become weaker and sleep a lot more when
they reach that stage, too.

In some ways infections may be a blessing.  If it gets worse, you
might consult with the doc about whether extensive treatment to
prolong her life would be what she would want, or whether it
might be kinder to let the infection take her instead of "saving"
her to die slowly as her body functions deteriorate.

d