Hmmm.. you had me thinking right there. I went through the chapters regarding Rafaela and that incident. I think you have a point. It might have been something to do with someone interfering with the soul link since when Rafaela apologized to Luciela about not being strong enough, Luciela's reply was "That's ok, it's not your fault". Of course that could be just to comfort her sister but IMO it could carry both meanings.
Now I had this crazy idea which made me very excited! What if what we all believe to be a killing hug from Rafaela was actually nothing but a forceful pull back to revert the awakened Luciela? Now, why would I think that? Because in Jean/Clare reverting incidents we see a huge yoki explosion and the one being pulled shows painful expressions (We didn't see Jean's but I suppose it's possible since it was put as a cliffhanger + Clare saying it was a painful exhausting procedure). We also saw those yoma veins surfacing the faces of both. At least the one pulling does for sure since they have to synchronize their yoki with the AB and the AB already has his veins surfacing. All those factors where shown in Rafaela/Luciela's incident! Plus I never thought an AB (let alone an abyssal) would die from just getting his/her back broken! Heck, even Ophelia survived a broken neck while being a claymore. The fact that Luciela's arm fell like she was dead could be nothing but from fainting after reverting back forcefully. This theory could also come in favor of what we think Riful is aiming for and that is to neutralize Priscilla.
We never really heard Rafaela saying that she "wants" to kill her sister or that she hates her. It was all Rubel's assumption. Also come to think of it, why would Rafaela try to kill her sister using that bear hug? Luciela was powerless and all what Rafaela had to do was swing that claymore and cut that neck of Luciela with ease and save her the pain she would go with a broken back.
You might ask about how did Rafaela think that an AB could revert back, I think it's obvious. She was taught how to use soul link for this very same purpose! to revert back the AB. So I don't think it's that far fetched. What Clare and Galatea did was a crude soul link in that it only reverts the AB while a complete soul link controls that AB throughout his awakening process (before, during, and after).
Now, I know all of this is wild speculation. I wouldn't be surprised if Luciela and Rafaela showed up sometime in the future together as normal claymores. This of course could pose a dangerous plot-destroyer which is that ABs can be forcefully brought back which is just not right since our fab 7 could just go wild and revert back as they please (Although knowing the fab7 would never risk such a thing) but if my theory was right, I am sure Yagi wont ruin it like this. Maybe he will show us that Luciela reverted but died afterward as it was done forcefully. Who knows. I am just excited right now!
