any advice welcome

evening all im a little concerned about my one girl so any help / advice would be greatly recieved. a few weeks ago she started eating her own poop 

i asked for some advice on here but didnt really get an answer as to why she does this or if it will harm her, i have just gone out to put them to bed and have noticed 2 very watery poos with a little white in it.

she seems in good health still running run the garden when they are out and pacing the run when i walk up the garden to let them out. the only thing i have noticed is that she has been digging in the run and found some sand which has tiny little pebbles in it which is coming out in her solid poops, all else seems fine she is still laying everyday and still the happy little hen i had from day 1.

i have looked through the pooh pictures but dont really see any similar so hopeing someone has been through this before.

thanks for your time sorry if i go on im just worried 

hi tigerwren
They have access to 2 water drinkers all the time which i add cider vinegar to so there should be no reason why she should be without a drink. i got them in october when they were 15 weeks old so that would make them roughly 7-8 months old. in the day they are in a run which is 6x6x6 the floor is just soil (mud after the rain yesterday) they have plenty to keep them entertained. i feed them on mixed layers feed the crum type stuff, they have one of them grit block things but they never bother with it. how else can i get more grit into them if thats what she needs?? thanks for your help and understanding from a newbie 

Just a thought. You mention that you add cider vinegar to your waterers. Maybe this is the problem if you have a hen that does not like it. Also I think those that use cider vinegar do not add it all the time. As you have 2 water drinkers maybe you could try one with and one without.