Thank you everyone for your words of sympathy and comfort.  

This is the first time I've lost an animal (except a childhood dog) and also
had to make the decision to end a life.  It almost seemed easier to me in the
first 24 hours.  Now I somtimes find myself second guessing.  Living with that
decision is so hard right now but at the same time I can't fully say I regret
it.

No one in this newsgroup ever judged me but some things were suggested that I
chose not to do.  The 2 things I could've done but didn't were the brain scan
to confirm the tumor and the anti-seizure meds.  12 weeks ago the vet would
only consider the anti-seizure meds as a last resort.  The prednisone did
eliminate the seizures and bought her those 12 extra weeks without any
episodes.  When I started seeing hints of seizure activity last week, I was in
a different place.  More important, my little girl was in a different place.
In those 12 weeks I saw a very slow decline in quality of life.    Things like
having to give her 2 meds twice daily to keep her bowels going because she
wasn't going often enough and once strained so hard she fell over in her mess.
Not making the box sometimes.  The pacing, circling.   Not being able to jump
or see. Having to confine her because she was falling off things she was still
able to climb onto in the beginning.  Or her long thick fur beginning to knot
because she couldn't groom like she used to.   She never used to let me brush
her and was fanatical about her own grooming.  But in the end, she would
happily lie there and stick her leg up in the air, then off to the side for me
to brush like she used to do for herself.   I was more than happy to brush her
regularly and spend as much time with her but it was also breaking my heart to
see this slow decline.  And what quality of life is, I'm learning is a very
subjective thing.  Some people can argue that being able to eat and eliminate
is the basic foundation of quality of life.  But beyond that is a very grey
area that is so hard to call.  

In her last few days, I noticed she stopped kneading or purring when I spent
time with her.  Then on Saturday when I saw stronger indication of seizure
activity, something inside of me just snapped..   I couldn't do it anymore, the
agony of making a new decision every week or two, getting deeper and deeper
into this. It was different 5 years ago when she had fatty liver disease, there
was hope for a full recovery and weeks of nursing, she did fully recover and
had 5 great years.  But this was much different, a slow deterioration, a dismal
and inevitable outcome.   I think if I waited much longer to make that call,
the memories of her remaining days may have broken my heart far more than the
loss itself.   I am thinking that this is the key to this whole thing, the
memory of knowing what I allowed her to endure versus the memory of giving her
a good life.

This all sounds like I'm trying to justify myself/decision to you all but I'm
really trying to justify it to myself.  And maybe get some words of comfort
from someone who was once in the place I am now.  I hope this back and forth in
my mind is normal and will eventually subside.  It is so ironic because
yesterday a good friend also made the decision to end her cat's life and she is
struggling with the same things I am.

Thank you for listening and my words of sympathy go out to everyone else who
has ever lost a pet.  Until one experiences it I don't think it's possible to
truly understand the depth and heartbreak of this loss.  And I keep telling
myself that the tears I cry are only for myself because she is in a better
place right now.