ECOAS Mash for Mash's Ortenaus Costume Dress, since she resembles the ECOAS Jegans in said costume dress.
It's acknowledged by Scathach in her trial quest, and Blackbeard calls her this a few times.
These names originated in the official preview gag manga by keikenchi, where they were derived from the term gudaguda, meaning "tiring" or "tedious" (as Fate/GUDAGUDA Order itself was) plus male (-o) and female (-ko) name endings.