Could he shoot her legs to stop her? I am very sure; they know how to aim and shoot the target.
The same argument; when Chihuahua tries to attack police, or Pit bull tries to attack police. Police does not need shoot to kill a chihuahua. Pit bull, it's a must to kill when pit bull forwards and attacks.
Police have the right to eliminate, terminate, or stop the threat, but they can use the common sense, also.