I'm very sorry. What a complicated mess. You had your reasons for keeping your distance from your aunt, and I've seen pressure in my own family to reconcile when people had NO IDEA what they were really asking. In other circumstances I'd say your aunt was a bit of a drama queen for leaving such a message, but since she just lost her brother (I'm guessing here), it's understandable.
You showed a lot of grace in calling her. Big virtual internet hugs, I'm sorry about your dad.
I'm so sorry for your loss MrsA. I don't think you have any reason to feel guilty at all. It sounds like you really tried to make it all work, so please don't feel guilty.
As for your aunt, I think you need to talk to her when YOU are ready. If it's easier for you to send her a message right now, then do that. You don't owe her an explanation or apology for this. I agree with ESF in all of this.