Sibling to Sibling Contact

My daughter texted my stepdaughter the other day to tell her about her new boyfriend. No response from my stepdaughter.

How hard is it to write a couple words back in a text? Especially since my stepdaughter is permanently attached to that cell phone for texting all the time? It's not like she has to go out of her way to text back. She can text without even looking at the phone keypad while holding a conversation with somebody! I saw her do it.