Lady was the ideal Weihnachten present for Darling.
The Encyclopedia of Walt Disney's Animated Characters: From Mickey maus to Hercules by
John Grant

Walt Disney Character Beschreibung of Lady from "Lady and the Tramp" (1955)

The opening sequence in the movie, when Darling opens up a hatbox to discover that the gift which Jim Dear has gegeben her for Weihnachten is a puppy, Lady, had its origins in an incident in Walt's own life. Many years before he had forgotten about a abendessen datum with his wife, and some sort of gift Von way of a peace-offering was definitely called for - something really special. His solution was to give her a welpe in a hatbox. It worked: she forgave him. It was an event which Walt knew he could someday put to good use in a cartoon.
The model for Lady was a cocker spaniel called Lady which belonged to the animator Hamilton Luske. In reality, however, there are two "Ladies" in the movie - the newborn welpe and the young female dog. Both are evidently the same animal, but the older version has quite definite fremale characteristics while the welpe is, like all puppies, essentially sexless. However, the underlying character - loving, basically trusting, good-spirited - is much the same.
Although Lady is not such a strong character as Tramp, she is Von no means the useful cipher that so many of the Disney central characters are: romantic she may be, often terrified and confused she may be, but there is also a deal of steel in there, as we discover during the consecutive sequences when she first tells Tramp to go away and leave her and, second, attempts to break her chain (she is finally successful) in order to chase and fight the ratte and thereby save the baby. Barbara Luddy voiced these two aspects of Lady's character exellently, being Von turns romantic and stern; she also managed to convey Lady's fundamental decency - the voice alone tells Du that Lady is the sort of dog Du would ideally like to own and let your children grow up with.
Lady is decent, but she is no naíve innocent. Without really skirting around the issue, Disney managed to get over the idea that Hunde do in fact mate, even before "marriage", yet in no way is this at all offensive. That, for the studio, was a minor and generally ignored triumph.
One trivial point of interest: Lady has a blue halsband, kragen while both Jock and (in due couse) Tramp have pinkish-red ones. No "blue for a boy, rosa for a girl" here!
It's amazing how a plateful of spaghetti goes to a lady's head.