[3] Lähnemann is the daughter of the theologian Johannes Lähnemann [de], and the granddaughter of the German medievalist Eleonore Dörner [de] (née Benary) and the archeologist Friedrich Karl Dörner; she grew up in Lüneburg and Nuremberg, Germany.

In 2015, she was appointed to the Chair of Medieval German Language and Literature at the University of Oxford.

[2] 2015–2024, she spends two months a year as a Senior Research Fellow at FRIAS, made possible by co-funding of the chair by the VolkswagenStiftung, the DAAD, and the University of Freiburg.

She brought a new linguistic and interdisciplinary angle to Reformation Studies in Oxford, completing the team of experts - Lyndal Roper and Diarmaid MacCulloch being counted among them.

The author Angelika Overath dedicated her novel Sie dreht sich um[17] to Lähnemann.