I'd like to know that.
You know I've suffered half a dozen bereavements directly, and been peripheral to a number if others over the last five - six years, and i can honestly say that some of my own reactions, and some of the reactions of people I've had to inform have the appearance of "inappropriate". However, what it actually is is usually a combination of shock, awkwardness, loss for words, attempts to fill an awkward void with anything, everyone's response and behaviour is completely unique and I have come to learn it means very little in the context of what a person really feels when the shock wears off.
"You're joking" is a common one, with often a really nervous laugh, followed by mortification because it's an involuntary response.
"Giddiness" might simply imply she had nervous energy and might have been over compensating in trying to help. I've directly experienced that too.
Plus verbal diarrhoea, people trying to push cups of tea at you, scrabbling for tissues etc.
Dealing with death is fucking awkward for everyone involved, even professionals.
When my Dad died, I informed his housing officer who had brought tenancy documents to his hospital bed to finalise his permanent tenancy. I informed her over the phone, and she said "Oh, I am sorry, he did look very poorly, I didn't think he was going to make it when I saw him". Yes, it stung, and I had her on speaker phone so the friend with me had her jaw on the floor. I could have complained, but what's the point? She'll get a mouthful one day if she says something like that to someone less jaded and cynical than I.
I don't think she's going to murder anyone though.