Yikes, sounds pretty bad. But it also kind of sounds like your interaction was the latest in a long line of these confrontations over the course of her having a guide dog. (Not with you, with others.)
If you wanted to dissect this more analytically, I would say that despite your cordial wording, the opener wasn't as polite or neutral as you intended. "Why do you walk your dog without a harness" is guaranteed to elicit a defensive reaction, especially with the followup of "it puts people in danger." Right there she's hearing that you are calling her a menace, and closes up. She didn't handle this well, but whatever else her issues, I'd guess that was part of her reaction. I can't condone or explain the subsequent screaming though.
Hard to tell if this is salvageable, but would it be worth it to try? "Hey Ms. X, it's YourWelcomeOrMine from the first floor. I didn't mean to accuse you of anything the other day. When [Dog] is off harness, he sometimes [does specific behavior] and I wasn't sure if you were noticing that it's almost knocked a few people over. *[if necessary]* Of course I'm not saying you shouldn't walk your dogs, but in your position I'd want to know that. There are a few senior people living here that would be really hurt if they fell down. Can we figure something out?"
That may be optimistic. Given how your last conversation ended it's unlikely to make things worse, though. And it's not a situation either of you have to accept as is without at least trying. My understanding is that guide dog handlers also get training in managing their dogs, for example this text document from Guide Dogs for the Blind:
$1.