Poor Gertie. She’s just watched her son murder a man someone, who, while she may not have liked him (or maybe she did) was close enough to trust with important things, intimate things.
She’s watched a man die at her son’s hand. Then her son is relatively cavalier about it. Polonius’ blood is probably spilling out all over the floor and Hamlet is unconcerned. She didn’t raise him to be this way, did she?
If I saw someone kill another person right in front of me, in my bedroom, no less – you can bet I’d be wringing my hands. I’d be pacing, too. And trying to breathe deeply.