Elizabeth is an American Cocker Spaniel

Elizabeth is definitely an American cocker spaniel. Cockers have very long full ears. It is part of their identifying characteristics along with the "stop".
There are two types of Cockers, the American and the English.
I have had 3 cockers so I am familiar with the breed. Elizabeth is a parti-colored Cocker.

There are 3 categories, Black, ASCOB and parti-colored. Ascob stands for Any Solid Color other than Black. Ascob could include champagne, silver, and any shade of red or reddish blonde.

The "stop" in American Cockers is more pronounced. English Cocker Spaniels are almost the same, but have a longer snout and not as much of a "stop".

The Americans bred the English cocker to look more fragile and have a fluffier coat.
They are very lovable dogs and quite high maintenance.
It really doesn't matter what kind of dog they had in the book (if they had one) because you know how directors and producers are. They will change it to whatever looks and acts best on film...