My very least favourite storytelling device is drama driven by characters not talking to each other. When a whole load of angst happens because people who would normally talk to each other don't, I just hate it. Presumably over the summer Giles would have filled in Joyce on everything from S1&2 that she needed to know. Maybe not the events of Prophecy Girl as that as that would be too much at that point. But about everything with Angel, what Buffy has been going through since he turned including her guilt at not having killed him before he killed Jenny. That when Buffy said she needed to go save the world, again, she was being literal. Joyce would also have filled Giles in on everything that happened with Spike and between them Giles would come to understand the deal Buffy made to let Dru go and explained to Joyce how much that would have hurt her too. He and Joyce would have speculated on what happened and Joyce would have learned that Willow was trying to re-ensoul Angel.
So when Buffy showed up at the end of Anne, Joyce and Buffy would surely have sat down and Joyce would have let Buffy in on just how much she has come to understand. Then gotten Buffy to tell her exactly what happened after she left the house that night. Buffy, might have been reluctant initially but she would eventually have explained it all to Joyce. They would have reconciled much better at that point and Joyce would have called Giles, had him come over and either had Buffy explain to him what happened or explained it to him herself. Then either Buffy or Giles would have told the rest of the Scoobies. They would have sympathised, while also letting her know just how much it had hurt them that she hadn't gotten in touch. Xander's 'kick his ass,' comment would have come up and moved on from. Then over the next few days Willow would have told her how much she missed her friend while she went through her big changes over the summer but it wouldn't have been a recriminatory thing, just a truth that would help Buffy realise that even though she was hurting, her actions hurt the people who love her. And when Angel fell out of hell, Buffy would have been less inclined to hide him.