I get it. And it seems like everybody's pissed at this chapter, so the manga done fucked up in expressing itself - and I think the release pace and the way the half-chapters were broken up doesn't help. But she isn't mad that he doesn't remember and she isn't giving him the cold shoulder; she's avoiding him out of shame. Why? Let me recap:
From her perspective, when she was at her lowest and isolated in the hospital, a boy in her class that she didn't know came to visit with her friends and offered to make a gift for her. The gift helped her get through it all, mentally. It was the most special, personal, important connection she'd had with a boy and she completely falls in love with the idea of him. Time passes. She meets him again without knowing, starts falling in love with the real him as she gets to know him, finally goes out with him and has a great time on a date, and confirms that they're the same person! And right at that emotional climax, when she wants to pour her heart out and and thank him and have a moving, fated reunion, she's hit by an avalanche of a revelation that it was ALL one-sided.
"Oh. You were actually giving those out like candy? And some of those kids left such a strong impression that the boring ones like me weren't really memorable? So the story in my head about being by saved by you; my love; our connection, I... just imagined those, on my own. Because I'm an idiot. So you're even more saintly than I thought... And I, by comparison, am such a small person that I got overwhelmed, lashed out at you, and ran away in defeat, functionally nuking our nice day out and our burgeoning relationship.
I want to die, now." She feels awful, foolish, guilty, humiliated, and pathetic.
She doesn't blame him at all.
So to that end, she gets points from me for even getting out of bed and coming to school. As for why she won't talk to someone who means so much to her? Well, the realization that she doesn't mean shit to him, for starters.
And the friend, Douguchi? She acknowledges that he's right to find it unreasonable but unashamedly has the policy of "I have my friends' backs,
especially when they're wrong," making her a first-class bro. Even if I kind of want to hit her.
And I would have been way worse at the MC's age - I would have made such a mess out of this if I were in his shoes, getting my feelings hurt and cutting off all contact like you said, and also turning the thing with Douguchi into a screaming fight it the middle of the hallway. Ugh.
Yeah, I guess my point is that the manga's doing a bad job if what everyone takes away is "God, they're such bitches."
Why does it feel like I'm defending it, then?