Autistic sister being rude and unpleasant

My mother made breakfast for my sister and I this morning, we're both on the spectrum. My sister was staring at me and hardly saying anything and frowning at me throughout the meal. She's staying here about a week. On the first day she came she was all sweetness and light but now she's become quiet and seems quite touchy. She makes a big deal out of almost anything I say, so I'm scared of talking about anything. Like she's picking everything apart in detail.

I said to her I could hear a lawnmower outside (just to make conversation as sitting in silence with someone staring is awkward) and then she said she couldn't, and it was probably a fan in the bathroom. She said this in a condescending way because I'm her little brother. She has a hearing impairment too so I didn't bother correcting her as I didn't want to embarrass her. Whatever I try to talk about at the moment, she makes some point to correct me. She can never seem to let a conversation just flow comfortably. When she corrects me she slows the conversation right down and talks in a slow, drawn out way and stares at me to check I agree with her correction. I feel like her ego is inflated.

Anyone have any insight into her behaviour?