I feel so blah

So yesterday I found out my childhood pet passed away. He has been living with a different family for the past year because the place that I lived didn't allow dogs. So I texted my sister last night who is 13 and told her and my stepmom(who I haven't spoken to in a year and a half) messaged me back basically yelling at me because her and my dad decided not to tell my sister. How was I supposed to know? I thought she had a right to know about it. And she is 13, she isn't 7. Death is a part of life. Was I in the wrong?