Yeah, my parents were both pretty self-absorbed like this too. I was more like Shiho's sister in high school, really angry and under a lot of pressure. I escaped to a far-away university too and looking forward to it was the only thing that got me through high school. Now I'm an adult I barely talk to my parents, even when I was almost homeless I would have rather gone to a shelter than gone back home. Yep, everybody in this manga needs therapy.
One thing I don't think Shiho completely admits to is that when she got away from her parents she probably wanted to completely forget her old life and that's why she lost touch. So it *is* a bit selfish for her to come back and want to be friends again after leaving Miwa to deal with her own issues alone. Shiho wasn't even the most supportive friend in high school to Miwa, she was only ever thinking about her own problems. But it's up to Miwa if she wants to accept the apology or not and how much she wants to reconnect. Does the old love still exist? Does she still have rose-coloured glasses on?