If your wife passed an English Test at B1 level or above then she will not need to re-take the test.
The only requirement is the test she took must still be listed on the latest UKBA approved listing.........which IELTS does.
All's good to go
I'll try to locate previous posts with 'chapter and verse' as stated by UKBA to enable your research and validation.
Your wife must include her certificate with the application.