If it was that easy nobody would create zombies.
Soulfire, Harry may be the only wizard with access to Soulfire at this time, and therefore the only wizard able to do this once it has been conjured. Soulfire should not only allow him to stabilise his constructs, but to control them as well. Sue would be uncontrollable until he puts some Soulfire in her, unless Butters turns up with Bob.
I think Freydis getting to ride on Sue would make her upgrade Harry to at least an 8. She wouldn’t be the first woman to be impressed by a dude with his own means of transport.