@Chttrbx_ Her knowledge of magic is too little to make any confident accusations about Anastacius just talking out of his ass. That's why she needs Lucas there asap. However, since Anastacius knows Lucas is a problem for him, but Athy doesn't, she has no reason to think she should try to hold Anastacius there because she has no idea the depth of how far Anastacius has gone, and how much Lucas could potentially incriminate Anastacius. If she keeps Anastacius there, he could have more snide comments to make that could worsen the noble's opinions; plus, it would come out that her father is actually bedridden which is also not what she wants. If the emperor is seen to be on the verge of death, due to black magic, while the original and obviously powerful previous emperor is still standing, the nobles could take the chance to just get rid of her father if they decided to, because even if Anastacius is a user of black magic they also have no way to fight him since he clearly knows enough to come back from the dead.
She has no idea if her magic explosion is a result of something more sinister or not. All this back and forth would've taken place in the span of 5-10 minutes, which is very little time for her to realize that Anastacius is talking bullshit, that her best plan is to keep Anastacius there, and spin a saving grace for Jeannette. She not only has to think about what her next step is, but three steps after, since Anastacius has obviously gone of the long con and she also wants to protect Jeannette and the Alpheus family.