The house had shown up a few days prior and despite being wary, there was no way that Buffy wasn't moving in. It was her old house, the one she'd grown up in, the one she'd lost her mother in, the one that was supposed to be debris in the bottom of the Sunnydale Crater. Inside of it are all her mother's furnishings and art, things that Buffy had cherished as the parts of her mother that she had left. They were all things she'd had to leave behind when she'd left Sunnydale.
Perhaps it's a coincidence that Joyce's ghost shows up shortly after the house, shortly after Buffy and the others move in, but it doesn't feel like coincidence. It feels like purpose and it has Buffy rattled. She'd refused to talk to Joyce, aware that she's not real. She can't be real because that's something that Buffy still can't handle. Instead, she focuses on moving in. She doesn't have much from here because she hasn't been here that long, but she is moving many of the things from her old room to Joyce's room. Alcide is going to move into her old room and she's going to take over Joyce's room, which is totally perfect now that her mother is haunting her (not). Maybe that's why she's being haunted. Maybe she'll ask Dawn to try some sort of cleansing something or the other. She doesn't realize yet that anyone else can see Joyce (and she kind of hopes that Dawn can't see her because she doesn't want Dawn to be upset by it).
Eventually she'll end up locking herself in her mother's old room and talking to her ghost, but that's for later when Joyce wears her down, when she finally can't not speak to her mother. Right now, she's trying to distract herself, to keep busy, to focus on getting herself and everyone else moved in.