Phone call from the vet:

He's taken lots of xrays, sees no signs of pathology. Thought she might have a collapsing trachea but that is not the case. She seems to have typical old dog lungs and nothing physically wrong.

She seems to have a decreased ability to handle stress, which happens as dogs get older. And might be the whole problem here. Her licking/chewing of her front legs is a stress reaction, much as we might bite our nails.

She may have allergies and we will consider benedryl for her. We might also have to consider anti-anxiety meds.

He is going to review the xrays again when they're dry to ensure he's read them correctly.

I will talk with him again when I pick her up. He really just wanted to call to let me know there was nothing "serious" that I'd need to worry about. He figured I'd be sitting here fretting about it, and he was right.