While a sibling will usually get a small boost in the admission process, a school is not going to admit a student who they don’t feel will succeed at their school. And as others have said, someone who is actively dealing with mental health issues is not a great candidate for BS. The best thing to do is to focus on schools where you will thrive, and when its your sisters time to look at schools, she needs to find the best option for her.
As a side note, I suggest you change your screen name if it contains your actual name.