Abstract: The Deep Underground Neutrino Experiment (DUNE) far detector is sensitive to around MeV electron neutrinos through electron neutrino charged-current reaction with argon. This capability is a unique window into the electron neutrino component of a Galactic core-collapse supernova flux. Extracting the properties of the supernova spectrum is, however, limited by the poorly-known electron neutrino-Ar cross section. We propose a data-driven strategy that leverages Boron-8 solar neutrinos and muon-decay-at-rest neutrinos as standard candles for this process.These calibration samples constrain both the low-energy and high-energy components of the cross section relevant for supernova detection.Our method reduces the reliance on nuclear models, which can bias the extraction of the spectral parameters by as much as 300%.