Sorry your hen is unwell.No, she doesn't go the the nesting boxes at all. She sits in the corner of the pen under the waterer, drinking constantly which all makes me think its not an egg. But, like you said it can't hurt to treat for it.

Symptoms sound nothing like egg binding to me... and the double yolkers happening still often would be an indicator that something is a miss in the reproductive system... more like Salpingitis, EYP, or ascites as mentioned.
The constant drinking could also be a sign of slow crop... I would suggest checking before bed, removing feed and water at night, and check again in the morning to see if it is empty or has any lump left or squishy-ness indicating such. Sometimes it can be a combination of things.

http://www.theveterinaryexpert.com/backyard-poultry/egg-yolk-peritonitis/
Hope she recovers quickly!
