Free choice grit, clean water and gentle crop massage seem to help. 

 Yes. It is best to try to remove the bulk. I do this at night. Hang the hen upside down by the feet, quickly massage the mass down towards the mouth. Its like forcing vomit. Youll have to be careful bc this will block the airway and she could breath it in. So only do this for about 5 seconds, then right her up and let her rest for 30 secs.repeat you got most of it out. Its possible she could have an impacted crop caused by a foreign object or of veg like grass hay. Those can be difficult to remove. Check on her nightly and force vomit her if needed. Additionally, you can feed her a mix of yorgurt, garlic and spices. There are recipes online. Careful with garlic as it can be toxic to birds at high levels... 

 Also be prepared to get vomit on you. Sometimes she will inhale a bit and cough and shake her head to get it out, which makes vomit bits fly everywhere!