I'm not doing Weight watchers so I don't do points, but the Sonoma diet limits fat and restricts the type of fats used. Avocado is an allowed fat.
Since you ate it you own it
and should probably count it as calculated .
But if it makes you feel better look up the nutritional value of 1/4 avocado and subtract that from the total fat,calories and fiber. Then calculate the salad and decide if that amount of food was "worth" that amount of points. Then add the avocado as a separate item. An occasional serving of a high nutritional food like that can only be a good thing in my mind.