Bunny Antibiotics

Question
I just got my 3 month old rabbit from a pet store a week and a half ago.  She seemed to be very healthy this whole time, but when I got back to my room today, I noticed diarrhea in her cage and she was very lethargic.  My normal vet (who hadn't even got a chance to meet her yet) was closed as it was after 5pm when I got home.  I found an after hours emergency vet and took her where they gave her fluids since she was so dehydrated.  The also told me to give my bunny 2cc of the antibiotic smz-tmp twice a day starting tonight.  When I got home, my bunny seemed to be a little better since she was actually hopping around a bit as opposed to just sitting around.  I fed her the medicine and within 10 minutes she had stopped breathing.  I tried to resuscitate   her but failed.  I just buried her but I can't help but wonder, could the medicine killed her??  Is it possible? She is a Lionhead, and I am aware that this bread is quite new, so not much is really known about them yet (at least I have not found much online).  Plus she is very young, so the illness could have killed her but I still find it bizarre that she seemed to be doing better until after I fed her this smz-tmp medicine.  Please let me know if you have ever heard of rabbits dying from taking this medicine, or if I am just over reacting.
Thanks

Answer
I'm so sorry for your loss.  And it's so much more difficult when something so doubly unexpected like this happens.  

Also, it's a natural reaction to suspect that the medicine may have caused her death.

I can't give an exact answer, since I don't have the specific medical background to do so.  

But the digestive system in a rabbit is very sensitive and more so when things get out of balance.  Since your rabbit was having diarrhea, her digestive system was possibly unbalanced bacterially to begin with.  Sometimes, it doesn't take much at all to push their system over the edge.  It's a real balancing act vets have to do when treating rabbits.  Particularly when there is some digestive problem.  

Diarrhea in and of itself can be fatal to rabbits, so you did the best thing for her by taking her to a vet.