I am so sorry for your loss.

My rats get pizza all the time and I have never had a problem, so I highly doubt that's what it is. My first guess would be pyometra, if you said her stomach appeared to be bloated. Did she suffer from Myco symptoms at all? Another thing is maybe she ate a piece of fabric and got a blockage. Is there anyway you can have a necropsy done to find out what caused her death?