I just lost a 5 yr old Netherland Dwarf October 05 and it was devistating to say the least. I never measured their pellets (mistake) so didn't notice until too late that she wasn't eating as much. I took her to the vet as soon as i did notice it. He x-rayed her and she did indeed have a hairball. He had her on 2 cc of fresh organic pineapple juice (from health food store or Meijers) twice a day. You also have to monitor dropping so you are aware of intake and outtake. My Sweeties droppings ended up very tiny, some tinier than mouse droppings.
Vet had her on benebac, nutracal and reglan, plus the pineapple juice. She eventually died, but I would take her to the vet asap, before it is too late. Also like your doing; unlimited grass hay and whatever she will eat. Her sister is now going through the same thing, took her in yesterday as I read a post on one of my forums about malclussion of the teeth. She did have sharp edges on one side. Due to mislignment of her teeth which is common in the dwarf rabbits. She has an apt tomorrow morning to get them filed. But vet said that he could feel a hairball too.
Could the longer dropping be the night fecal, which is longer and softer and pretty smelly. That is normal for rabbits and usually they eat these, but not always.
I am also giving and gave both rabbits lots of different greens, as much as they will eat andhave had no loose stool or any negative results. Also feed them some dry oatmeal, even a organicdog bisquit, give her preety much whatever she will eat, an please deep us posted for all to learn from.
I discovered this because she wasn't eating her pellets at all, but when I soaked them and let them get soft, she ate them all and her fecal has looked good the couple of days i did that. Good luck!