Willow as part of the Trio...

[Taralover]

and she meets Tara and of course the two would fall in love. Plausible?

[Hemiola]

I assume you mean the "Evil Trio" headed by Warren.

Yes, it's plausible. In fact, it's close to the way I originally thought that Season 6 would go, i.e., that Willow would eventually become the "Queen" of the Evil Trio, but would ultimately be redeemed and saved by Tara. This would have made much more sense the actual way that things turned out.

[Zooeys_Bridge]

I read a fascinating meta about the Scoobies relationship and parallel to The Trio in Season 6. Two, actually, and they can be found Here and Here. The second provides illuminating thoughts about Season Six that although still don't make me enjoy it per se, it does make me appreciate and understand it more.