Bitches tend to be smaller than dogs out of the same litter..and with the smaller dog's they seem to reach there full size earlier than your bigger crosses..i had a beddy grey x collie grey many moon's ago and it hit it's full height by 8mth old which was 21"..does she have much knuckle left to grow out on the front wrist that is usualy a rough indication of how much growing she has left in her..