I obviously don't know Squid at all. But, I think that when someone we know and love is approaching death, we often start to review our own lives. Sounds like Squid has a lot to review, especially with all that's gone on with the two of you over the past year. If Squid has refused counseling and other external resources, I doubt that she has developed many new coping skills to handle life's stresses. And, death of one's parent is definitely a major life stressor...whether you liked or loved them, or not!
It might be that it's all Squid can do right now to just "hang on" while dealing with her mother's death. The two of you have been making progress. But when we're stressed, we tend to fall back on more familiar patterns of coping. It takes a lot less psychological energy. So, her shutting down may be the best she can do for the time being.
It's got to be soooooooooooo hard to see this "setback" after all the good progress the two of you have made! I think I'd be much more concerned, however, if there wasn't at least one major external factor (mother's impending death, annniversary date of affair, etc) that COULD be tied to her current withdrawl and change. It's hard "not knowing" what exactly is going on, but there remains the distinct possibility that it's a temporary response to some major stressors.
Sometimes there can be a "silver lining" to these stormy times. (Although I get sick and tired of all the storms! One can only handle so much before it starts flooding!)It can be an opportunity for each of you to learn more about yourselves and your relationship as it stands now. Perhaps the progress you have made (Squid included) but weren't seeing clearly...maybe additional insight into areas that need to be given priority and worked on further. Maybe Squid "needs" her current pain and struggle to help her see that she really does need to get some outside help (counseling).
These are just some of my thoughts. Not sure if they're applicable or not, but they came to me while reading about your concerns. A friend recently reminded me that healthy living isn't necessarily about making the river run straight and clear. It's about going with the flow, rocks and all, side tracks, dry spells, floods, and those wonderful times of splashing in the water, taking in the beauty of nature, and just "being". I keep trying to make that river run MY way! <img src="/ubbt/images/graemlins/rolleyes.gif" alt="" />
