I am so sorry to hear of Squishee passing over, I really am.
It always hurts when we temporarily have to say goodbye to a beloved bird/best friend/family member.
Please try to console yourself with the fact that you rescued Squishee and that your life, not to mention hers, changed so much for the better.
It's times like these when I wonder who rescued who...
I know that your heart is aching now, but please don't give up on rescuing birds who might need rescuing. We've rescued birds, too, and have lost them, and our hearts seemingly broke. Hearts patched together after a time.
Rescuers are special people.
You'll see your beloved Squishee again when it's time, I know you will. Meanwhile, I have a sneaking suspicion that she may be flying around happily on the other side with some of her many flying friends, including some she may know from this forum.