Is there a term for the pose when a woman covers her breasts with her hands (like for a photoshoot or movie)?
I think a term that is coined lately for the pose is handbra. (Also, hand bra or hand-bra.)
(Especially with reference to a woman) making a pretense of shyness or modesty that is intended to be alluring: she treated him to a coy smile of invitation
You might also consider the adjective demure. It can mean
affectedly modest or prim; coy
It also can mean
Modest and reserved in manner or behavior.
Its application to a bashful nude would be a bit ironic.