Welcome to the board, city fried hunter. I'm a part timer on the board but there's a lot of great people here to learn about all the aspects of hunting.
I don't know that you did anything wrong. It's hard to eat meat that your not sure about. I'd probably took her backstraps, they would have been ok to eat and that way she wouldn't have died for nothing. The tumor may have been from a previous wound that healed poorly but you never know and the bloating was probably gases in the stomach and she was probably ok but is the chance of food poisoning worth it. Other folks on the board here can tell you more about spoiled meat.
I'll tell you how I handle deer at dusk. If I'm not positive of a double lung shot, I don't take it. Trailing a deer at night is risky business and alot of times its better to save the deer for another day. A double lung shot deer is not going far but even a deer shot thru the heart might cover alot of ground before falling. There are alot of variables you have to think about before taking that dusk shot, is it going to rain, is the moon going to be bright, do you have help, do you have access to good tracking lights, i.e, lanterns or portable flourescent, both are good for spotting blood at night. The other thing, are you an experienced tracker or is somebody with you an experience tracker. You even have to think about what your schedule is for the next 24 hours to figure if you have the proper amount of time to find the deer. A poorly shot deer, gut, etc. should be left alone for at least 4 hours before trailing. Of course, you have to consider the temperature. Anyway, I didn't mean to get into writing a book but taking a life is worth thinking about. Good luck to you hunting and I hope you enjoy the board.