At this point of the plot Lamia is supremely stupid.
Not about Aquila, really. Given Aquila's antecedents, in her position I would be also suspicious as fuck about this guy and his sudden change of side.
@Amarrez and
@Kisa24 pointed it clearly, the guy has a well deserved fame of being dangerous and unstable, I would be very cautious if I were her (and I like better if the trust becotween MC and ML is slowly earned instead of immediately given because Twu Wub or whatever)
But girl, you know better than anyone that your younger brother doesn't have the talent, nor the competence or the disposition to be the next family head, and yet you insist because you are pretty sure that with effort and a bit of sockpuppetry from your hand he can do fine. No
manita, he cannot and we won't, no matter cuantas bolas Uri le esté echando, he is doing his better but his better isn't enough
and you know it. I get why you are trying, but even if we the readers saw how well that choice went in the other timeline by just reading the title of this webtoon, you should stop your delusions that your brother will become as competent as you in way less of the time you managed to be competent yourself.