This kind of full body shake is usually associated with one of three things: attempts to dry off, ear problems and stress. Since I am pretty sure she hasn't been soaking wet for three days (!) we are left with the other two. Sometimes ear problems are deep inside the canal and can't be seen just by looking at the external part of the ear. You may want to have your vet check the ears with an otoscope which will allow for examination of the entire canal and ear drum. (For example, grass awns can get into the ear and may migrate deep into the canal--this would be irritating, but we wouldn't see anything externally.)
For stress--this is harder to pin down, because it doesn't always seem obvious what can make them feel stressed, and sometimes the reasons don't make sense to us as humans (my cat for example, gets extremely stressed out by the door buzzer--doesn't make sense, and you would figure he would get used to it, but there it is!). It the ears show up clear, you may want to try some natural calming remedies to see if this helps. Here are some ideas to try:
--->DAP, which is a pheromone based product used to relax dogs in stressful situations. It comes in different forms such as a collar, a spray and a diffuser. There are differing reports on how well it may work, but it is a safe, natural product, and won't hurt her. Here is a link to their website with more information: http://www.dap-pheromone.com/gb/DAP-The-secret-to-happy-dogs/All-about-DAP-R/The-DAP-R-product-range
and liquids: Composure is one formula for stress that I have had good success with, your vet may stock other brands. http://www.vetriscience.com/composure-soft-dogs-MD-LD.php
Bach's Rescue Remedy comes in liquid form and can works wonders: http://www.rescueremedy.com/pets/
I hope this helps give you a couple of ideas to look into, please let me know if I can answer any other questions.