She hits them both, and they explode into clouds of exhaust smoke, but the spin leaves her at an awkward angle while she lands, and when she touches down a third familiar bull-rushes her.

And concentrate - 

She summons another sword intersecting with the familiar.

Success.  Familiar vanishes.

Her barrier-sense leads her across several more chasm-jumps, and up and up and up.  She's getting close.

'Kaylee, how far are you? I'm nearly at the heart.'

'Getting there.  You'll probably get there before me if you keep going but I can catch up quick if you do.'

'Alright. I want to end this thing as quickly as possible, so I'll get started without you.'

She proceeds.

Soon she emerges into a great spherical chamber made of the roofs of a hundred towers like the one she's just ascended - it's not quite the center of the barrier, but it's close.  Gravity is misbehaving, down is toward the inside surface of the sphere; opposite her is an enormous creature like a cross between a spider and a sea urchin, backhoes for legs and folding tower cranes for spines jutting out at a hundred precarious angles.  It is, unmistakably, the witch, and it's crawling toward her across the surface of the sphere.

Vulnerable to a giant flying sword?

It probably wouldn't notice a single thrown sword unless it was really big.  Dangerously big, larger by far than anything she's seen before.  If she doesn't want to take that big a hit to her soul gem, the other option is probably closing in and hacking away at innards.

That's gonna be dangerous, but she has an advantage on healing, so.

She bounces up, avoiding moving parts, trying to move at the witch's innards - and when she gets close, aiming a sword at whatever looks most vulnerable.

As she approaches, it swings wrecking balls at her, but she's fast enough to dodge.  When she wounds it, it screams, a horrible sound like a metal girder tearing, and begins to claw at her with enormous backhoe-legs.

She dodges what she can, parries what she can't, and tries to cut off a few legs at the joint for good measure. 

She takes out a couple before a backhoe with a shovel-claw as big as her entire body scoops her up and flings her across the sphere.

It shudders, then begins tearing open the tower its standing on, folding up its spines and burrowing downward.

She slows herself down midair, bounces back over, and pursues.

By the time she gets back over, the tunnel the witch carved is seething with familiars.  As soon as they see her they start swarming toward her on all fours.

Swing through those, manifest a sword to skewer that conveniently clustered group, toss that one away from her with ribbons when it nearly gets behind her - 

She has the feeling that Kaylee will catch up before she makes it through this.

And, indeed:

'Lianne, I found the witch, it's on the inside of a big globe, coming up out of the floor - where are you?'

'Trying to follow it, I don't know how quickly I can get through these familiars - be careful, it's pretty difficult to take on at range.'

'I'll see what I can do.'

She leaps and rockets through the air toward the witch, conjuring up arrays of knives in midair and sending them spinning through the air toward it.  As she gets closer, she conjures a pair of Bowie knives, but before she can close the gap it swats her aside with one of its legs, then heaves and twists its entire body to send three enormous wrecking balls in her direction.  She only just manages to scramble to her feet and jump backward out of the way.

She goes in for another approach, this time from above: she leaps into the air and springboards off of nothing in midair, shooting down toward it at an angle that she hopes won't let it send another wrecking ball toward her.  Instead, it scoops up a bundle of familiars and hurls them at her; she stabs one in midair, springboards off another, and flings knives toward it and the remaining two as she shoots away.

She lands some distance clear of the witch, and grimaces.

She spots a flash of gold rocketing across the chamber toward the witch.

"Lianne?" she calls out, in ordinary speech.

But no, it isn't Lianne - the color scheme's the same, but the new girl came from the wrong direction, and Lianne isn't that fast...

Whoever it is has a long, slender sword in each hand, and manages to slash apart three or four more flung familiars in midair before she lands on the witch.

"Who the hell's Lianne?" she calls back.  "Listen, I don't care if this is your territory - " she stabs another familiar and leaves the sword embedded " - I've spent months tracking this thing down, it's mine, get your own."

"I'm not - we can work together, can we work together?"

"You any good at range?  Keep these crawly fuckers off me!"

"Got it!"

She is pretty good at range, in fact, and she's been practicing taking shots from midair; she manages to jump and hover and prevent any spare familiars from getting close to the mysterious new girl.

'Lianne, somebody new showed up, she's taking care of the witch and I'm keeping familiars off her but I don't know if she can finish it on her own or not, how are you doing?'