why on earth should Mrs Ferrars wish to commit suicide?

[masonsouth]

In a novel, Mrs Ferrars is dead, but a character says:

-Why on earth should Mrs Ferrars wish to commit suicide?

To refer to a past thing, we use SHOULD HAVE DONE STH; to refer to a dead person, we should use the past tense; so why is the tense: SHOULD MRS FERRARS HAVE WISHED?

[Alan]

Normally, yes, but in this case the speaker is clearly imagining the past situation as a present one for dramatic effect (cf. the use of the historic present).