Ah, now this isn't a problem to me. Dawn's story in this episode follows on from the issues we have been seeing build up for her since before Buffy's death. Her importance, her relevancy, whether she is real, whether she matters at all
is part of her story from the get go and this episode just continues it. I'm invested in that story growth and development, even if I don't personally relate to it. It feels right to me to see some wider context for her then, to get to see her with her peers and how she relates to them when she has been feeling so pushed aside, and even if it is just as a one-off. Seeing how Dawn gets caught up into desperately seeking peer approval, ignoring dangers and signs she should recognise in Justin just emphasises this issue of feeling adrift, separate to the others and how willing she is to fit in to feel wanted.
It also highlights how unsettled everything is specifically because of Buffy's return. Not only is everyone not focussing on Dawn any longer, but discord is starting to become apparent. She walks in on Tara and Willow arguing in the kitchen and seems disturbed by it. And then later when Justin finds out her sister is the slayer he upsets her by attributing his interest in Dawn to that, "Your sister's the slayer? I totally get it! I knew there was something about you." It must be really hard to be able to see that Buffy's return, which she will have been so happy about, has caused such disruption too. With Spike no longer playing the same role in the group, Willow and Tara fighting, Xander's and Anya's relationship shifting (even if it seems positive at the moment), and with Buffy distancing herself as well, everything is fluctuating again and Dawn doesn't know where she belongs, if she matters, whether everything is going to be good again.