Our Gertrude is quite a woman. I would like to have seen her as the actual ruler of Denmark, instead of just the spouse. I mean – she does not have to attempt to calm Laertes down. She could scream and panic. She could throw up her hands and call for help. But no. She steps in, right from the start…tries to defuse the situation. And given that Claudius has to ask her twice to let him go, she also physically gets in there.
Now – why she’s defending Claudius so resolutely when she presumably has worked out a little of what Hamlet’s been talking about is a little bit of a mystery.
I think it’s likely that Gertrude has a strong sense of self-preservation and realizes that Claudius is the best horse to back in her current predicament. I mean, to her knowledge, Hamlet is gone. He’s been sent to England. She’s left with a (possibly, as far as she’s concerned) king-murdering husband. How to survive in the circumstances is to stick with what she knows. And it would appear that Claudius is pretty good to her – if not good for the country. Sure, he’s murdered her first husband but that’s in the past. How would she fare with a King Laertes? Probably not well. He’d probably have her executed.