Very simple. There is a difference between opposing intervention in Syria and actively supporting and promoting Assad and talking about how great a leader he is.
She doesn't support Assad. She has criticized him for being a dictator.
Also the fact that she’s a staunch supporter of a far-right, nativist, theocratic, anti-Muslim party in India is a legitimate concern.
She's not a BJP supporter. She also met with Congress Party members.
I seem to recall that at one point she was going on about how Assad was going to bring democracy to Syria, which is naïveté at best, covering up for dictators at worst.
I in general hate whataboutism, but until the Mister Bone Saw carved up khashoggi, everyone in the West treated him as a liberal reformer, even while he committed war crimes in Yemen far worse than any Assad have committed, at home he execute Shia clergy, whose only crime was objecting to the second class status of the Saudi Shias (while the Assads had expanded the rights of Syrian Palestinians* and Syrian Kurds). Yes if Gabbard believed Assad was pro-Democrat, she was a sucker, it in that case she’s one sucker among many in Congress, and she at least wasn’t in the pocket of a Regime, who funded anti-American terrorism.
The truth is that Assad is not a nice man, but there’s little reason to single him out negative among Arab leaders for human right issue.
*Syrian Palestinians have the most freedoms among the Palestinian diaspora in the Arab World, and it was Assad senior, who gave them it.