I've been avoiding jumping into the What's Under the Door pool until now, but here it goes:
It's not her husband, but rather it's the picture that was hanging in the reading room. We see it for first time during our drunken exploration. It's on the left-side wall:
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Then, it was on the floor the day after the whole M&J saga:
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That evening, Bella glanced at it while they were walking out of the room:
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The morning after the Cathy drama, it's gone. This is the same morning MC glances under the door.
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In the enhanced screenshots several folks have posted of what's under the door, it looks like the shoes are the bottom part of a picture in a frame with a cloth on the floor in front of it, which might have been covering it up and then removed by Bella so she could look at the picture.
As for what the picture is, now you're talking wild theory territory. But what the hell - I'll go there, too. It's her kid. The shoes could be Chuck Taylors or even hiking boots. The stepping stool and low mirror in the bathroom are obviously for a child. And, the shirt she loaned MC for yoga was short, maybe for a pre-teen. How old was the kid in the picture? Where did he (yes, gender assumed) go? Why is she packing away stuff that reminds her of him? And what's the deal with the axe (ok, probably related)?
The answer to all is "I don't give a crap." Of my 9 saved routes, Bella's will always be the first I play through when updates are released. And I can say that with the confidence of knowing she's not hiding a corpse or an invalid next to her downstairs bathroom.