I believe, well it's just my view on this, with speaking and listening, if she can clearly understand what the interviewer is saying and can respond properly and express herself in speaking in English, then that is good. She just needs to practice in conversing in English as often as she can. That will make her confident. For example, make sure that common mistakes like proper use of he or she will be corrected, coz that's one thing that is easily noticeable. Start from there and practice practice practice.
I always correct her as you say. We converse loads every day. Thank you