I liked to see how a loathsome character, for once, gets the treatment she deserves by readers. What never fails to happen, however--and what naturally gets my attention--is that of course, there will be those defending that loathsome character in a conspicuously contemptuous manner.
I, for one, hoped that Kaiser would kill her--the opportunity for on sight is gone, and I know that he won't (he already stated his desire to interrogate her, and most Japanese authors are sissies who love aggressive, masculine females anyway), but it's nice to imagine it. That said, it's all this Regina character deserves: without an iota of thought, she executes multiple terroristic actions all to lure Kaiser out and "get the rust off his blade". Never mind how she could have seriously wounded or even killed Elsa (since she's so committed to only fighting for realsies~), or how that surprise attack of hers that went through a building could have nixed everyone in it in that attack's path (since, of course, in the middle of a populated city neighborhood is the only place for that sort of thing in her mind).
In fact, the first would have been a good enough reason: a sword isn't the toy she says wooden swords are but sees her own highly functional one as. Once one is drawn--and Regina just loves this fact--you can reasonably expect someone to be maimed or killed. If I were in Kaiser's shoes, and loved those girls as much as he is depicted as loving them, there would be no room for explanation; no room for justification, no room for forgiveness, no room for rationalization, no room for ifs, ands, or buts--there would be no reason for her not to die.
And why not? Regina is clearly a loose cannon with a highly dangerous combination of negative characteristics: she's both profoundly bloodthirsty and profoundly stupid and/or foolish (i.e., has no second-order thinking ability). Japanese authors like girls like her, though--since before Love Hina. It didn't escape my notice, by the way, that while Elsa squarely got the beats put to her, Meryl (in her 20s if I recall correctly, but looks only a hairsbreadth from 10) drove her off without a scratch.