What type of cancer was the furball diagnosed with :-(

Sorry to read about Buffy.  If the cancer is untreatable or the cost is
prohibitive then you'll have to bring yourself to have her put down.  It is
sad, but time does heal.  We had to put our old cats down within 3 months of
each other and got new cats who now tear around the apartment like lunatics.
While no cat could ever replace Buffy, having a new kitten from the SPCA can
go a long way toward easing the pain.