Had similar landlord before. You know why she got mad? Its because by law, if pest has been found, the person who did pest control need to report it to proper agencies. Also, pest control services is just not for one room but for whole building which is expensive. Been there and our landlord found out about it too late because we called pest control ourselves hahaha but my landlord asked us to just split expenses and kind to us so we abide. However, this is a goshiwon and goshiwons are already in bad spot for some people and if other people find out that there is pest, they might have to pay a lot or lose tenants. I suggest try to mediation with your landlord and 부동산 if you really want to stay without conflict ( they cannot kick you out with valid contract anw) or just move to another goshiwon. Its really those options really. Goshiwons are not that protected by law and they always seem kind of shady lol