The other Democratic candidates are kooks who have no chance of beating Trump. Gabbard is positioning herself to either be a dark horse Democratic candidate or a third party candidate.
As a third party candidate, she would just be a spoiler, enabling Trump to more easily win. As the dark horse nominee coming out of the Democratic convention, she would be an effective candidate running against Trump. She is a lefty kook like the others, but she is taking “principled” positions to seem moderate. Time will tell whether she is able to pull the Obama trick of getting elected based on a phony moderate position. As Obama said of himself, “I just let people see themselves in me, like looking in a mirror.”
She has stated that she will not run as a third party.