I guess I would ask...what do YOU need in this situation? Your needs count, too.
Just because she texted you doesn’t mean you have to respond. You did, understandably so...and she showed you that nothing has changed.
NC again, yes? This is only me, but I would send your nephew a nice card and a great gift and skip the graduation. It’s got too much potential for drama, given her history.
I’m sorry this is happening again and I hope you can take back your serenity.