[@TheWindel]

Judging form a bit of your wording, you may not be familiar with series beyond what research you did for your character? In BnHA, there is a central theme building that an idolized hero society has its problems. Deadlier, villainous Quirks are often looked at a bit negatively. For example a character with a mind control quirk is deemed "evil" in the eyes of characters and suggested they'd make a good villain even though he wants to be a hero. There is actually some oppression to characters in the series based on their quirks, essentially. 

So the issue arises from your character actively wanting to pursue a more dangerous application of her quirk. Brain hemorrhages are really scary and by actively pursuing this application of your quirk, there is an implication that your character is okay with killing so long as it stops a villain because a person's survival after a brain hemorrhage would be out of your character's control. Thus, the staff Ishin would actively attempt to dissuade your character from pursuing this application of your quirk.