IMO it's very important to be able to tell the difference between lethargy/listlessness and the snake just chilling because she's going off food for awhile.
Does she still tongue-flick like normal when she is out of her tank being handled?
Is her muscle tone good? ie; Does she still grip onto you appropriately if you pick her up?
Is she still reactive to environmental change? ie; Does she try to move away like normal if you go to pass your hand over her head or touch her on the nose, or something else that would normally get an evasive response?
Those are things that might be an indicator of something being wrong. If she's just spending more time hiding, it could be that she's going off food for awhile and conserving energy.