This may well be a sign of readiness to give birth - it may be a placental discharge. Look for signs of nesting also -> may look for a safe place to give birth e.g. in a cupboard, closet or under the bed etc. As long as she is eating and drinking she should be OK although this may also reduce shortly before birth. If the discharge has a greeny colour to it and has a foul smell, then it should be checked out as maybe there are dead kittens in there which need to come out asap. I am assuming that she is current on her vaccines since there are many viral diseases that can cause stillbirths and abortions.
Hope all goes well.
Martin Slome DVM
Centre Street Animal Hospital
7700 Bathurst Street Units, 40-42
Tel. (905) 771-9855