IELTS has only 2 year validity yes but once you have achieved a B1 qualification in English then you dont have to retake another test, I stand to be corrected on that.

I have an ESOL Certification that was awarded to me by Cambridge after I passed the ESOL Listening and Speaking Level 2 exam last year. ESOL has no expiration, I enrolled meself in the college and paid 200 odd quid at first but they returned the payment after I applied for the student support fund which I am eligible due to my circumstances. In short, I got it all for free. The test only lasted for 30 mins, very easy to do, just a conversation and listen to a recording.

I suggest you to ring your local college and see if they can do an assesment for your wife. Ask if your wife is eligible for student fund and go from there.