Meditations on THMÊ (MĒT?)

I’ve been studying the Hermetic Order of the Golden Dawn literature and practice for over 2 years and over the past year, I’ve been meticulously working through the preliminaries for the Neophyte SI ceremony. I’ve recently come to the final 1/3 of the THMÊ meditations, which is the 1/3 that actually carries the namesake. Through my studying of external sources on Coptic, it seems I’ve found incongruity. The HOGD refers to the Coptic goddess of Balance, Justice, Truth, and Order as the name THMÊ, which seems directly descended from the Greek goddess’s name, THEMIS. However, outside of the Golden Dawn and adjacent literature, I can’t seem to find a single historical attestation for THMÊ in Coptic. The most confusing part of this all has been that Coptic does in fact have a name for that very same goddess. To the Egyptian ancestors, this goddess was known by the name Ma’at. The historical Coptic name seems to be something like MĒ, MEI, or possibly even MĒT. These variants obviously descended directly from the Egyptian tradition, so my real question for anyone knowledgeable enough, why did the members of the HOGD make up a seemingly fictitious, Greek-derived name and etymology for a goddess that already has a relevant name in the Coptic tradition?