Sister issues

My sister has been slowly withdrawing from our family for awhile now. Whenever someone tries to reach out to or talk to her, she'll get mad at us our ignore us. She used to speak with one of our siblings, but now she's starting to act short with them too and I've noticed that it looks like she's losing weight and I have absolutely no idea how to help her. If anyone knows what I should do or who I can go to for advice I'd really appreciate it.