Do you think I was mean for telling my sister that her friend’s breakdown isn’t my problem?

So my older sister hasn’t heard from her best friend in a week she last heard from her was last Tuesday. She has called and texted. She was having some mental breakdown. She was telling me about it and I just looked at her and said, “So what do you want me to do about it? That isn’t my problem. Just wait until she messages back. I’m sure she’ll text back.”
I know it sounds mean but I have my own problems to worry about. I am 17 and got to worry about my upcoming senior year of high school.