That's my guess, but reading MN law for involuntary manslaughter, it requires "conscious action": "... consciously takes chances of causing death or great bodily harm to another..." If she thought she was tazing him, she didn't "consciously" risk his death.
https://www.revisor.mn.gov/statutes/cite/609.205
How does “involuntary” fit with “consciously”?
I think I read that their manual says not to taze someone operating a vehicle. If that is correct, I imagine it could be said she was being reckless by attempting to go against protocol on that—and then the result that she inadvertently caused was death.