Was she egg-bound. This is common in colurbids more than boids. And if she just laid eggs one could of cause internal problems.

Wont know for sure iwth out tests done. But breeder does owe you something ater 3 weeks. No healthy snake should die in 3 weeks unless husbandry problems could be the problem.

On other side 88-90 is WAY to hot for colubrids. 80-84 is all they need for a warm side.