If you are familiar with working with a pendulum you can take a map and starting with an area where you think she might be hold the pendulum over it. If the pendulum stops swinging and begins to turn in a small circle you have located the area where it is likely that she is located. If you don't get a response on that area of the map, then move on to another and repeat the actions.
I hope you can find her safe and sound. It sounds like a very sad situation.