I think you said you'll have a letter from her? - make sure it includes her contact numbers, and suggest to her that she is phone-reachable around the general time you will be going through immigration. It is far from unheard of for IOs to phone and make sure the stories match up.
Obviously, she (like you) needs to tell the truth, but you might want to alert her to the possible suspicions an IO would have, just to make sure she doesn't inadvertently say something that could be badly misinterpreted.
As Britwife says, hopefully it won't come to that, but it's far better to be prepared.