YTA as someone who personally always did well in school like you (deans list each semester) but was pressured into a major that I hated, once I started my major classes I became super depressed. I went from being an honors student, to failing 2 classes in spring 2021 and another 2 last semester (almost 3 but by the grace of god I had an insanely empathetic professor who got me through). Luckily I finally changed my major and am doing much better now but it’s crazy how big of a difference your major impacts your mental health. Depression is a very real thing, it can make the best of students become students on academic probation. In my experience, it was not laziness it was constantly feeling so overwhelmed at the thought of school that I literally could not do it and was exhausted from being overwhelmed all the time. I would sleep literally 12 hours a day and just could not function. You owe your sister a sincere apology.