Searching for Manga

hi, I am looking for a manga where the main character is a girl who is being taken advantage of by her sister at a magic school. She is always doing magic for the sister from the shadows and also uses magic to disguise herself then heal a prince. FMC had to not help her sister during one class practical because if she did bad she would flunk and her sister preformed bad and blamed it on not feeling well. using the disguise magic and healing is strenuous and she ends up fainting and found by a black haired classmate. please help!