I wonder how much time passed before the Coast Guard went out looking. They are based right there in Gloucester, so they didn't have very far to go. The reason I am wondering is because if she's deceased, and her body temp dropped, thermal imaging may have not worked if her body temp matched ambient temp if they waited a while, and although I have nothing to base this on, my guess is they waited til all other avenues were exhausted, (her bring with a friend, over someone's house visiting , checking cell phone records, etc.) which may have taken many hours.
Drones are great, and this time of the year there are no leaves on the trees, however a drone may not be able to spot someone under a pine tree, which there are a lot of there.
It was nice of the neighbor to help like that.