Happened before and was supposed fixed, but this patch has brought back the bug where the thornwake staff either causes full damage to kerillian upon reaching max- or just out flat blows her up stone dead like she’s unchained. It also causes her damage sometimes just casting thorns above the 2nd threshold.
Please see the pinned post: About the Vermintide 2 - Bugs Category to see what information to include in your report.