Otwo-- provide her with reassurance, plain and simple.
Nothing you could say will have more impact than reassuring her that your love and concern for her will never change. Having legitmate reasons for fading away from the organization do not, and should have nothing to do with that, and I am sure from all you've said they do not. Anything that could interfere with that relationship, we know, is destructive. But it will take time for her to get to that realization.
Say little unless she asks, and recognize the denial "he's still a good witness" is a defense mechanism. That's why the reassurance is so important. AND let her talk and really listen to what she says and process it. There is no more effective way to help anyone than to make them feel heard. Use the phrase, "what I hear you saying is...." and then reflect her thoughts back being careful not to add anything, then just continue listening b/c she will likely keep expanding on it. If not, just sit and reflect on that thought and give her the space to do the same. Hope that helps you. Be patient, it may take a while.