As this ESPN-W article concisely states it:
With an 8-0 victory over Indiana on Saturday, [Michigan's Carol] Hutchins got her 1,458th win and passed Fresno State's Margie Wright as the winningest coach in Division I softball history. Hutchins, who is in her 32nd season as coach of the Wolverines, has a record of 1,458-474-4.
The University of Michigan athletics website, MGoBlue.com, features a "Hutchins by the Numbers" infographic.
One can argue that the B1G is not a deep conference in terms of quality opposition, and that this helps Coach "Hutch" pile on the wins. However, the Wolverines annually play one of the nation's toughest nonconference schedules.
The aforementioned ESPN-W article notes that Arizona's Mike Candrea is only slightly behind Hutchins, with 1,450 career wins.