I know a Libelle is light on tow, especially for a Pawnee.
But as a Pawnee tow pilot, I fly pitch attitude, keep the eyes outside, the ASI is for reference!

We did have a similar incident here many years ago, not our operation.
Tow pilot got slow on climbout, brand new DG300 stalled on tow below 150ft AGL, glider released and hard landing destroyed the glider.
Pilot walked away, slightly sore.

BillT.