Shorten her lifespan and what, deform her uterus? :wesobi:
It's not plausible, it's not remotely likely that Karin would just... die giving birth. It's right up there with Sarada being the spawn of Suigetsu and Karin and only slightly below Sakura adopting their bastard kid out the goodness of her heart.
For it (death by childbirth) to make much sense, she'd have to be a) on death's doorstep prior to giving birth or b) the birth itself is used as an opening to kill her in a weakened state.