I am not sure. Measure her from the base of the neck to the base of the tail. If it is between 14 and 15 inches it should fit. It is really really cute.
I have a similar coat, same brand, and my 7lb chi takes a small. It's a little big on her. tried a medium on her and it's huge. Love this coat, wish it were a small. of course my pup has 5 coats. lolol