No, she made the right decision voting for Mari. As boring as it is for us to see a 7-3 vote, as a contest it is better to make sure you are on the right side of the numbers at Tribal and do damage control later. Her vote didn't decide it anyway so there was no advantage in being in the minority vote unnecessarily.
Her mistake was taking so long at the voting booth. You have to appear decisive at tribal even if you are confused as hell. All she did was let the majority alliance know that she can't be trusted.