So therefor it seems to me, there are some forgotten pixels at this part of the gif, because there is no movement. :
But they do jiggle a bit, look at it more closely...not that I am against extra jiggling. 
Oh,, I did!
Very intensive - to find the "strange point".

And most of the time, when switching between the images you will find the move of the body, without this part.
And while watching the animation, this gives the impression I told about (Well, I tried to do so).
I've gotten way too much practice animating boobies while working on KI).

, please no!
This jiggeling is animated fine, but it's much too strong for this young girl (for not to say it's not needed).
What have I done - I shouldn't have mentioned it -

Edit:
I didn't want to, but I have to ...
so here is, what I think whould be better for
this lady
(who is young, has a not too big size and is wearing a bra):

No jiggeling and simply moving together with the body.