This is purposefully ambiguous - to avoid problems with censors - but also because the source of the humor is that everyone from Dick Van Dyke to the audience is left wondering exactly what the phrase means: does it mean Sally merely has a crush, or is it a reference to something else more serious (and physical), which could not be mentioned on TV at the time. The risqué possibilities are a good source of the humor - implied to those whose naughty imaginations would take them there, but not necessarily, and that tension is part of the humor.