I do not believe that any dismemberment was accomplished prior to Zahra's death and that it is not a cause.
I'm really struggling with the cause of death in this case. With EB's history of abuse, it's entirely possible that she went too far and stuck Zahra in a way that killed her. The dismemberment in that scenario, other than to delay the identity of remains, doesn't fit though.
But if she really was "found dead" and infection was present in the amputated limb and that is a possible cause, it might explain why someone felt it needed to be disposed of separately. But you'd think it would have been buried as well so that's where it appears that there is more than one person responsible for the disposal. Each person had their task and handled it differently.
If her leg was dismembered with the prosthetic on however, it kind of negates the possibility that Zahra was "found dead" from illness. If she were that sick and in bed, she would not have been wearing the prosthetic at the time of her death and there would have been no need to dispose of it. Especially to fit in with the kidnapped from her bed story.
Just random thoughts based on what we've heard so far.
MOO