The king should be removed from his throne, the little sister exiled to some farm (and her royal status removed) with that guy, forbidden to ever even come close to anyone she knows.
It is not summary execution like she deserves, but at the very least it is a punishment that royalty (and nobility) was sometime given as the biggest insult possible, worse than death in the eyes of many nobility throughout history (though for others it was regarded as lenient and risking uprising, but I doubt there is a risk of that here)
Both are incompetent. The fact the man didn't realise that her seeing her love resurrected in front of her would remove her maddened grief is moronic, at the very least the attempt should be made. I mean, if it fails, just pull that spell out again. But weak mind or not, she should not have done what she did, no matter the reason and I could easily believe she might have done the same even if she retained her memories.