Shannen Doherty flayed. There's a sight many of her past co-stars would love to see 🙂
Lets not forget the fact that Dark Willow was fuelled by her personal attachments. While emotions will power you so far they also become your greatest weakness as you don't think tactically, you act first leaving yourself open to exposure - pretty much like a boxer.
Also, Willow's spells usually took some prep time, whereas the Charmed Ones' powers were more instantaneous, so I think they would just overwhelm her.
The ONLY thing in her favor is that IF we say Willow is a witch the same way the Charmed Ones are (which you could say she's not a natural witch and this wouldn't even apply) Piper can't freeze her. Because if Piper could freeze her, game over.
The charmed ones have faced evil witches before.
Willow would be overwhelmed by the Charmed Ones. She wouldnt be fighting ppl who care about her or who had concerns about hurting her.
The sisters have the advantage of numbers, range & each of them has powers that can give Willow problems on many fronts.
Any energy projection she sends their way can be turned back on her by Prue or Paige. Prue & Paige could also attack her physical body in various manners from a distance.
Piper's temporal stasis & molecular acceleration attacks could be used to strike @ Willow w/ the environment around her (freezing/slowing down her physical movements or projectiles OR blowing the ground she's standing on, or blowing up objects around her causing them to crash down upon her etc)
Willow is a lousy physical fighter & would be less than no match for Phoebe in a physical fight especially if Phoebe has her premonition & levitation in tact.
the Book of Shadows would most likely be the tool used in Willow's final destruction/vanquish.