First, I'm very sorry about your boyfriend. I don't even know either of you, and you're both in my thoughts and prayers.

As for your sister, there is no definitive explanation. Maybe a text feels impersonal, but she'd be even more awkward in person and end up stammering like a blithering idiot. With texting, or even with this post, at least you can think things through and go back and edit out what possibly came out wrong.

She could be struggling with knowing what's appropriate and what isn't, and is unsure what to say. Sometimes it's hard to know the right thing to say. Sometimes there *is* no right thing to say, and even when you say and do the socially acceptable things, it feels like reading from a script.