A few months back NPR (radio) did a special piece on Laika. They even spoke with some of the scientist that were involved with her mission. Everyone of them wished they could go back and plan to bring her home. (thery were not stuffy about it or detached- they were emotional). While they were very grateful for the huge leap they were able to make in science, they deeply regretted how they handled bringing her home (or lack of). They were very sad. But I think that may be why so many people see her as a hero- thier hearts go out to her and they want so bad to have something better for her... of course she's passed on. But for them at least they can remember her well, honor her, and learn from thier mistakes.
After the Soviet collapse, participants in the project told the real story: Laika indeed was to be euthanized with a programmed injection, but she apparently died of overheating after only a few hours in orbit.
Several other dogs died in failed launches before the successful space flight - and safe return to Earth - of the dogs Belka and Strelka in August 1960.