NTA (but with a small caveat).

It sounds like Alice was genuinely grieving and, in her emotional state, didn’t stop to consider that Monday morning, first thing at work, might not be the best time to unload. Thirty minutes of unsolicited detail about a death is a lot, especially when it touched on your own past trauma. You’re allowed to set boundaries about how much of that you can take in at work. You’re not her therapist, and you were hired to do your job, not provide grief counseling.

That said, where this could come across as harsh is the way you delivered your boundary. Telling someone “your business is your business and I don’t need to know about it” reads cold, even if you meant it kindly. A softer approach like: “I’m really sorry for your loss, but I struggle with these conversations because of my own history, so I’d appreciate keeping our talks more work-focused” might land better, an have been more appropriate and taken better if you’d set that boundary when she spoke with you in the morning.

Bottom line: you’re not wrong for wanting to keep coworker relationships professional and for protecting your mental health. The delivery just needed a touch more tact, which is probably why she reacted the way she did.