None of us knew what to make of it… checked http://gowdb.com/ and no mention of it.
Someone did find a mention of her here: GoW Spoilers but way down the list of upcoming troops, with a release date of “Jan 1 2030” (I’m guessing this just means no release date has been set yet).
So how does this troop appear “out in the wild?”
Most important, how can I get a secret mystery troop that no one else has even heard of?
Full Knight team with matching banner, so probably no random assignment for fielding an incomplete team. Low team score, so probably no player who has been active for a long time.
Wild guessing:
Dev account testing new troop.
Summoning stones from the Forge may pull troops not yet in chests.