Sorry for your loss. That really sucks.
I had a snake pass very suddenly as a new acquisition. Because of the number of reptiles I own I definitely did not hesitate on a necropsy and viral testing. At the very least it will give you peace of mind
Regarding the breeder, you can't post a beware on MorphMarket, but if she was purchased through the site I would consider contacting support regarding the situation. You probably won't get anything from it but knowing they'll get a ding on the record. The new management has been alright about taking questionable breeders off the site