I’m sorry for your loss, OP 
At 17, I only emerged from my room for sustenance and to go meet my friends / boys.
My 10 year old DSD has just vanished to her room. I expect to see her properly again when she enters her 20s. 
But seriously, I found common ground with my SC over meal times when they will attend the table to fill their boots. I’m a good cook, so I learned their favourites and nailed them. But also, whether you can cook or not, SC respond very well to the occasional Maccies for dinner 
You can get a few words out of them then. Tell them stories about when you were a kid. Ask what they did with their day and nod along with enthusiasm when they say “nothing”… then don’t probe any deeper.
Never take it to heart when they don’t talk to you for days. They’re just doing their thing and they’re grateful that you aren’t interfering. My friend has SC that yell and swear at her. I’ve seen it. If mine are just existing around me, feeling peaceful and happy, that’s enough.
And, above all else, have a thing you can do if it’s all getting too much. Mine involves taking a gin and tonic into my en suite for a while. I text the DH for refills. 