My guess is the sudden realization that Blondie was looking forward to talking to Blind girl and is disappointed that she can't is what broke her. She was gonna bully the dog into hating the blind girl but that didn't happen for a lot of reasons and now after being berated by a dog of all things, she's at her lowest. not getting that 1 glimmer of joy of interacting with a human being is what moved the depression scales from tipping into full on nose dive into the abyss.
that or like laser nipples said, dog is giving her a "tonight you" look.