Baldric...that is how we learn in medicine , by speculating, by listening to what happens, discussing likely diagnosis and finding out who is correct in the diagnosis, at post mortem. An important part of learning and in medicine known as Clinico-Pathological Conference.
Chrissa, knows this quite well and that is all she is asking for.....informed ideas.....and that is what she deserves.
In a 14 month old baby who was well up until 24 hours before death is not going to be caused by a common condition.
However, there is a mention of her being sick the night before and if that was associated with retching then we may well have a clue. There is a condition known as Mallory-Weiss Syndrome, where the stomach lining tears during vomiting and the patient ( usually an adult) vomits up blood which can be torrential and life threatening.
In a baby one also has to consider congenital malformations ( abnormal blood vessels and tumours.
These are just suggestions that come to mind, but i would be very interested in the post mortem findings.