I'm so... sorry for your loss.
Like other's have said, I too have had to make that decision and it's one of the hardest things you'll ever have to do.
But you made the right one. Lexxi is no longer in pain and waiting for you at the Rainbow Bridge when you all meet again someday. Sending prayers to you and your hubby.
Lexxi did die too young, but you gave her a wonderful life in those 3 and a half years that she lived.
Take Care...