Question: Assuming that Ripley wasn't infected with the queen before ending upon fury 161, would the facehugger implanted the queen embryo into the dog/ox or use one of the prisoners assuming it can choose which embryo to deposit first.
Answer: It could be the Facehugger either has a short life span or a short period of time to lay her egg.
Answer: It was most likely just been implanted when the ship landed or being a Queen Mother would take longer to incubate.