my bitch was exactly the same,at one point I lost her for 36hrs she was found 14 miles away and thanks to a lady I got her back
She would never come back till she was ready I tried all the treats,a firm hand long leads the lot but as soon as she got her head down that was it GONE,Ieven thought about getting rid
I dont know what happened but she is a year old now and she has settle down nicely, and all ways comes back to my whistle
so what Im saying is just give it time keep on with the training and it should happen
GOOD LUCK