To be fair, Tara pursued a sexual relationship with Willow, while Willow was still waiting for Oz to come back. However, Willow is a big girl. She can make her own decision.
Tara liked Willow and would often compliment her, they hung out doing magic together which aided in the mutual attraction towards each other. However, when Oz reappeared on the scene, Tara was willing to step aside, telling Willow that she should be with the one she loved. Willow made the choice to be with Tara, Tara did not push her into that decision.
No I'm saying that Willow was going to make a decision that she didn't agree with and Kennedy stopped her.
I disagree. When Kennedy accuses Willow of sticking up for Buffy, Willow replies "I'm not". There's only two ways Willow's response makes sense within the context of the scene:
1. Willow WASN'T going to stand up for Buffy but Kennedy automatically jumped down her throat before she could say anything. This makes Kennedy look bad.
or
2. Willow WAS going to stick up for Buffy (or at least try and be more diplomatic) but Kennedy intimidated her into saying "I'm not" by jumping down Willow's throat (which is something she'd done in an earlier scene) before she could say anything. This makes Kennedy look worse.
It is not up to Kennedy to decide what Willow believes. If Willow chooses to side with Buffy that's her choice. Kennedy should not get a say. That is one of the biggest problems with Kennedy, she's too keen to insert her opinion where it's neither required nor wanted. She evens complains to Faith that she thought things would be "different" with Faith in charge but Faith isn't letting her have her say just like Buffy didn't. It makes the mutiny against Buffy even worse because now it isn't just about questioning Buffy's leadership but about Kennedy initiating the mutiny all because she wanted to insert her opinion and Buffy wasn't letting her.
Kennedy never sexually harassed Willow, She persistently flirted with her and Willow began to like her. It was all very playful, there's no harassment there.
By that logic then, Spike never stalked Buffy, he "persistently" pursued her until she developed feelings for him.
Kennedy continued to flirt with Willow even when it was clear that Willow was uncomfortable with it. That "persistence" is harassment.
I love Vi, but I don't think that could have worked. Kennedy was pushy, because Willow needed to be pushed. Vi was too muted. I don't imagine Willow would have noticed her. Kennedy was the right medicine for the right time. Similarly, Awulyn helped Willow get her edge back, but now Willow seems to be looking for someone more like Tara was.
I think Vi would've worked because she had a similar attitude to Tara. I'm certainly not saying it would be a long term thing, but it would make more sense for Willow to start moving on with someone like Vi than with someone like Kennedy.