These enemies are difficult enough to locate if you dont know how. Here is how you find a Ghul Matron.
First it needs to be night time. So go to a tower and advance time until it is night.
Then go to the location in this video. You may find other locations but i know for sure that they are here.
Go inside and there will likely be a Ghul Matron already inside. If not you will need to kill a few of the ghuls that are in there. When they start to flea stop killing them. They will burrow into the ground and eventually a Ghul Matron will come out.
As you can see from the video, its very easy to get overwhelmed by the amount of Ghuls. To make life easier its probably best to do this while mounting a Caragor.