Here is a quote from P&I about eggs and cottage cheese:
"Many patients ask why eggs are not allowed. The contents of two good sized eggs are roughly equivalent to 100 grams of meat, but fortunately the yolk contains a large amount of fat, which is undesirable. Very occasionally we allow egg - boiled, poached or raw - to patients who develop an aversion to meat, but in this case they must add the white of three eggs to the one they eat whole. In countries where cottage cheese made from skimmed milk is available 100 grams may occasionally be used instead of the meat, but no other cheeses are allowed."
So yes, it's allowed as long as fat free. I made a shake with low fat cottage cheese two days ago, but it didn't cause me any issues.