It may not have anything to do with her marriage situation. For all we know, she is loving life married to Tom. The magazines lie - plain and simple.

I thoroughly enjoy magazines like Star, People, etc., but you know...they don't always tell the truth. Or, at least, they overexaggerate it.
I don't know about you all, but I much prefer wearing sweats and flip flops to dressing all fancy.

Maybe she just wants to be comfortable. and plus, now she's on Broadway, which must be incredibly exhausting. So maybe she's just more concerned about taking care of her health than her outward appearance.
Or maybe she is depressed! I have no idea. But I think she's awesome.