If I recall, the artist actually was familiar with Cavaliers as well, or owned one, or something like that so I would say that may have influenced appearance, but I would always have understood her to be more “officially” likely to be a Cocker–Cavaliers were hardly known in the US back when that film 1st came out! Anything done by Disney takes animal faces and shortens the noses into a more babyish face–think of Bambi (actually I was just reading something recently about how the animators were pretty much forced to give Bambi as shorter little turned up baby face to make the character cuter…). so the fact that the nose is a bit shorter than a typical Cocker would really be neither here nor there I think–just an animation quirk for characterization.
All that aside–I think it is really surprising that breed clubs would promote a breed through its use in a film. I know most people who are dedicated to breeds, including and especially good health focused breeders, hope and pray their breeds will never be featured in a film because this immediately leads to serious over breeding and exploitation. The very last thing I would be doing would be reminding people that a character they like is apparently of such and such a breed! The main breeders who benefit from that kind of popularity are the puppy farms and puppy mills. Every single breed that is featured in a popular way in a film–Cairn Terriers in the Wizard of Oz, rough collies in Lassie, Alsatians in Rin tin tin, Dalmatians in 101 Dalmatians, the Chihuahua in the Taco Bell commercials–all of them have been subject to massive breeding booms where it is the puppy farms that churn them out and then create health issues for the breeds that can take them decades to recover from, if at all. :yikes
Cavaliers already have so much on their plate in terms of health problems that personally I'm glad if the general public thinks the character of Lady is a breed other than a Cavalier! Not that I would wish anything further on Cockers either, as they have a lot of their own problems and are lovely dogs, but Cavaliers as a breed are closer to my heart.
I guess it's hard too–because we all like to see breeds that we like portrayed in an affectionate way in stories, film, etc. but at the same time, it can end up so damaging for the breeds!