I don’t know if Singer has himself answered Timmerman (I searched but didn’t find anything), but based on what I have read of Singer, wouldn’t his answer be that yes, Lisa must go on saving drowning children? That she must attend to her bank balance only so far as necessary to maximise the children saved, and ignore such frivolities as the theatre? That’s what it comes down to, for Singer: using one’s resources to do all the good you can do.
I don’t know if Singer has himself answered Timmerman (I searched but didn’t find anything), but based on what I have read of Singer, wouldn’t his answer be that yes, Lisa must go on saving drowning children? That she must attend to her bank balance only so far as necessary to maximise the children saved, and ignore such frivolities as the theatre? That’s what it comes down to, for Singer: using one’s resources to do all the good you can do.