Original post by Forum UserCareful - she doesn't have a change of position defence because she had no knowledge. She had no knowledge, therefore she is an innocent donee, therefore, she will be liable to make restitution unless she has the defence of change of position. She does have the defence here because the boat sank.
The basic idea of this defence is to not make an innocent donee worse off than they would have been if there had never been any breach at all - if she had to repay £25,000 then she would be worse off as she would be out £25,000 and not have anything to show for it at all. That's different from Ian's case because he is not worse off by having to repay £10,000 - he's in the exact same position he would have been if he had never been given £10,000 since he had already booked the spa break.
Going to make it clearer with numbers. Suppose Mother has £25,000 to start, gets given a boat, it sinks. If she has to repay £25,000 she now has nothing and is worse off than if she never got given the boat. Suppose Ian has £10,000 to start with. If he gets given £10,000, spends it on his spa break, and has to repay it, then he has nothing. But he had already booked the spa break, and would have had to pay for it out of his own money, so he would have had nothing in any case.
Hopefully that makes sense to explain the difference?