Well, got some news and will be waiting on others:
Necropsy found that her heart was enlarged and she had hemorrhaging around it, also that her lungs looked abnormal. He said this could account for her odd breathing/mouth movements I saw on Saturday.
He couldn't say for sure if this was caused by a illness/virus or if this was a case of her just not being well (ie like when seemingly healthy twenty years olds die abruptly due to a brain hemorrhage) so I opted for a full histopathology on her tissues/organs: this will help determine if she has something that may put my other snakes in jeopardy. I won't know these results for 10-14 days.
What surprised me is that after examining her he considered her obese and mentioned by feeding regime could be switched around for healthier snakes. It was truly eye opening as I've fed my colubrids the same as many other people do and after what I've read many times over and I didn't have the slightest idea that she was so overweight. He mentioned that a 7 day schedule is too much for an adult corn and I should scale back to 10-14 days, and also feeding leaner/younger mice instead of the larger fattier ones will be overall healthier for the snake (which makes sense). I will be re-evaluating my feeding schedules/habits with my snakes after this. He didn't think her being obese had anything to do with her passing.