How long have you had her? What are the temperatures (warm side, cool side) in the tub?
Just looking at that photo, I have the impression she is sniffing the fresh air exchange from the vent-holes, & that IS something a snake would normally do.
But I'll add that most of these plastic tubs also have chemical odors (& possibly unhealthy) as they are not designed for living creatures but only intended for
storage...please keep that in mind- no matter how many people find these convenient & inexpensive caging for snakes. (I do not use anything other than
glass tanks.) Snakes have a better sense of smell that we do, & I personally don't like how storage tubs smell so I can imagine that it's even more noticeable
to a snake kept inside...anyway, I think that's what she is doing.