Hi Robbie I have been doing some research for you and the Channel Islands are the same as the mainland ie: the NMC will only accept IELTS as a recognised English test to enrol as a nurse here at Level 7 in all categories.
My wife is going through the same predicament as your wife. Although it's quite difficult to reach Level 7 - especially in academic rather than the general version of IELTS - it's achievable with plenty of study.
Just to let you know my wife has taking it twice and last time one of the scores was just 0.5 out and that's with a 9-month old baby to take care of
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Rest assured, with a lot of hard work, determination and support, she will achieve her dream. Good luck.