I could honestly talk on this subject for days - but the short of it is - Our Lady died, not because of the punishment due us all for sin - for in Her was no sin, rather out of Her great humility. Her humility would not allow Her to be assumend, body and soul into Heaven without first submitting to the same death Her beloved Son did, but also proving that by so doing, She, as our Heavenly Mother, submitted to that same death that befalls us, Her children.
That makes sense. Thank you.