it sounds like she has a particular 'need' which the company should take into account during this process. your wife may well have to do this course, but her employer should be made aware of her needs and cater for them. if they don't, they will be breaching their duty towards your wife.
for example, i am currently in the process of having to apply for my job again (due to cuts in the nhs) and i have mental health problems. as a result, i am now very stressed, terrified of losing my job, and feeling backed into a corner - which i hate and makes my mental health problems worse - and my anxiety levels shoot through the roof. as such, i have informed my employers ahead of time (and will have documentation to prove such contact), will tell the interviewing panel on the day and may have to have some time out (for a freak out!) during the interview if things go a bit wrong.
your wife will have to figure out what her needs may be (with the company) and put an action plan into place. but try and calm her nerves by saying they are also responsible for helping her as she has been happily doing her job for 15 years with no problems...and that she must be valued by them too. good luck x