I use the find my app to share my location with my wife but her location is never accurate. why would this be? Is she masking it some

There are a number of things that can lead to a location not being quite accurate. Not having wi-fi turned on, being inside of a building, and while you can still get location in some, certain building construction can be worse. Being in a large city with lots of high rise buildings is another. And lastly, what your definition of not accurate is. Emergency locations for 9-1-1 calls is generally 15-20 meters, and if she is experiencing poor cellular reception, it can be worse, hence the appearance of the blue dot for the phone and a large blue tinted circle around the location. Then it is generally proving the location of the last cell tower connected to and a range of location outside of that.