I'm not sure if any of you have bought a house recently, but paying the stamp duty is done by the conveyancer, so the question is really if she intentionally lied to them about an existing property, that is the one held in trust for her son. If it can be proven that she did, she has to resign and suffer the financial consequences. If she can prove that she took professional legal advice which was incorrect, then she should not resign, but pay the extra 3% plus any fine.