It seems like (and someone correct me if I'm wrong) when she makes certain movements--especially 1-tile movements to orthogonal spaces--her tail sweeps across an area (varying in shape by the orientation of her tail) and coils up any enemies caught by it. So the best way to get coiled up is to move to spots adjacent to a lamia's tail. Furthermore, getting coiled up near her upper body results in a special scene.
As a lamia, coiling enemies can be done with that same tail-sweep movement. This pins them within your tail, allowing you to drag them around, easily strike them with heavy moves, or whatever else you may have in store for them!
Viewing post in MonCurse V0.7 (+ Lamia) comments
Pretty complex so if you transformed, you need to get used to her form, she attacks when moving side to side or up to down (clicking her main body side, not the whole snake part), lamia movements is zig zag and when moving in one line movements, she get pretty slow, so don't get into tight spaces, though if you coiled yourself, you're pretty much invincible and take barely any damages, so I guess this is why the dev said it's difficult working on the lamia :V