As for her being manipulated...not entirely sure where that comes from, she was plotting with others(Bail Organa and Mon Mothma notably) against Palpatine.
To the Sand People thing, they are monsters. They aren't human in the sense that they actually care for anyone who they attack, I mean they train their youths to be killers, having them go out and torture beasts or humans(example Shmi). So them all being killed by Anakin, doesn't really make him a killer...he wasn't kill defenseless people he was killing monsters who go out, raid farms and carvans, kill/capture/torture the people and take their things.
She was easily manipulated in Darth Plageuis.
Sand people are monsters to certain people but tell that to the Sand People and their children. The Children can be seen as innocent at the moment but in time would be killers only through circumstance.. but that is an assumption. Tahira Veila was once a sand person but became a Jedi. Anakin despite avenging his mother, did avenger her with hatred, meaning he was no different. I understand why he did it but it doesnt make it right. Padme knowing this, and at the time, still werent 'dating' means someone can tell you at their first few dates they killed ferets because they were angry. Would you still be with them or think them a little weird?