She designed or discovered AB material which is used to create AB Swords and is also supposedly the first Knight.
Though her current status is unknown as far as the translated chapters go, some extrapolations can be made of her state.
Seeing the unlikelihood that Ingrid, an EX-Type Zero who used a Supernatural Weapon was defeated before the discovery of AB material, it's likely that the discovery of the AB material was before SE 367, or 62 years before the setting of Main Episode-0 Pray. But it's also mentioned that she was the one who gave the go ahead for the Arin defense system upgrade.
Presuming that Mother Knight is not a title that can be passed on, but rather a person, she's probably very old by the start of the Manhwa, and/or dead after the Battle of Arin.