I think the way Crests would function in Lore as a fascinating thing to think about, so I did think about it and here's my thoughts on that. Am mostly going off of vibes, the way the Crests change her moveset (Regular and Focused attacks), and such.
Yes I am aware that Hornet's animation of swinging her Needle (mostly) stays the same, but I'm going off the gameplay chunks of the movesets changing, so bear with me.
Hunter Crest - Literaly just Hornet's standart mentality and fighting style, she wields her Needle one handed with her hand around the center of the handle.
And after Eva does her thing, Hornet basically starts to see week points in opponents the more she focuses, and getting hit breaks her out of it.
Reaper Crest - After getting this Crest and whenever she uses it she decides to wield her needle with both hands, going for overhead and uppercut slashes.
When she binds her wounds and gets her buff I imagine her Needle's edge is wrapped in a bit of silk which is connected to her spool, and striking an enemy the silk on the edge connects to the silk inside the enemy, allowing the Needle to tear it out as it leaves the enemy's body.
Wanderer Crest - After getting this Crest and whenever she uses it she decides to wield her Needle as if it were a rapier, with her hand resting on the hilt close to the edge of the Needle, giving it less range but more precision.
If she has enough silk on her spool it will open up in the shape of a harp, and as long as she has has the spool open like that her Needle is wrapped in a thin layer of silk, most of the times it does nothing, but at random it will resonate with the harp on the spool to vibrate and enhance her next attack.
Beast Crest - I like to think with this Crest she just decides to go ''Fuck it'', puts her Needle on her back, and decides to weaponize her claws.
Instead of actually binding her wounds with her silk, I believe that the way it would work is that she wraps her claws in silk and as she tears into enemies for that short period, she decides to use the silk of her victims to heal her wounds.
She also gets a tad bit more agressive when she fights, I'd also imagine she wouldn't be opposed to going for biting her enemies.
Witch Crest - This one is weird, but I think the way she's holding her Needle with this Crest is by having her hand on the end of the handle, near the part where she attaches silk to it, for wider swings.
Her bind is rather simple to explain, she simply uses the remains of the parasite inside her to suck of life out of anything she hits to heal her wounds, and to get the remains of the parasite to act she simply feeds it silk.
Architect Crest - Much like the Wanderer Crest, instead of swinging it she uses thrusts, however her hand on the handle is around the middle, similary to the Hunter Crest. And she spins her Needle by having an insignificant amount of silk on the handle and simply reeling it as she strikes.
And the way she crafts on the fly is by simply having the parts be assembled by her silk. I also like to believe that while using this Crest she has a more fundemental understanding on machinery, which is why she is able to craft wherever.
Shaman Crest - This one is also weird. I believe that she hold the Needle's handle like she would with the Hunter Crest.
With the way she's able to just throw magic slashes at people, my guess is that she somehow manages to gather just enough energy, most likely soul, and let's it rest on the edge of the Needle until she swings. And, similary to the Architect Crest, I believe that when she uses this one, she has an innate understanding on spell's, to enchant their lethality.