Power Level Edit
Undefined, but presumably low. Akua is shown to be unable to defeat the Catherine Foundling as the Squire in physical combat, although her focus was always more on magic and trickery. Heiress often employs mercenaries or manipulates powerful individuals to make up for this weakness.
Heiress is presumably a transitional Name like Squire, which would fit with the Name referring to a person in position to inherit something.
Special Powers Edit
The name Heiress does not strengthen the user physically but it does allow the user to manipulate other through more subtle means. Heiress' power works indirectly allowing her to manipulate individuals on a chessboard. The name also seems to enhance her magical abilities allowing the user to spar with the Apprentice.