Please help - missing friend

My friends sister died over a year ago, then she got really quiet (as expected) and suddenly stopped coming to school all together. Then her socials all disappeared, her calls stopped going through, her brother disappeared, whole family gone. Theres no obituary or anything for her sister and there were no accidents that aligned with who/when to help us figure out what happened, just a grave location online, she never told anyone that her sister died I just found out after seeing her legal name in a yearbook. It’s been over a year, she was supposed to graduate with us last week, I miss her so much. I don’t even know if she’s in the country. What can I do to find out if she’s even still around?

I don’t want to disrupt her or her family, but I’m losing my mind. She was my best friend and now she’s gone, it’s like she didn’t even exist.