It was not just one area that would have had such a severe drop in population of Spirits and Evil Spirits, so it would more likely be possible for it to get noticed.
She would no longer be visiting those places anymore and would be leaving them behind, so it did not matter too much that others could notice such a change.
Their eyes would be drawn to those areas and maybe to others close by, but they would not search as far as the area Ash had moved to.
Even if they did happen to extend a search for some reason, it was unlikely that they would have the manpower needed to check out every location every day that she could visit.
If there were no changes that were similar to what she had done, then they would give up the search and move on.
