In her own mind, Buffy had already moved on. A home to go to, she thought, trying the thought out. Yes, she might as well call her apartment home, she'd spent enough time there. The disbelief that she glimpsed out of the corner of her eye caught Buffy by surprise.
The speculation about her state of mind left her frowning and pulling back, not exactly grateful to be exposed. Especially by someone who seemed to be suggesting that she'd met a different version of Buffy.
Grief is selfish, and Buffy wasn't ready to see understanding in someone else. She didn't see sympathy, all she saw was someone she didn't actually know, bluntly pulling up things she'd rather not think about. Maybe she ought to, but she'd left ought to behind in her other life. She wasn't ready to deal.
"I don't know you," she said ungraciously. No pretense there, it had all been stripped away.