So far, the only arguments against Miya seem to be:
1) Her father pays the bills so she should let him do as he wants and shut her mouth
2) She's not trying to understand her father
3) She's stayed holed up for a year and now has the gall to blame her father for coping in his own way
In order...
1) Is that seriously an argument? "I'm paying for your expenses and I'm your parent, so you have nothing to say"? That's a pretty horrible mentality to have, thinking that you're entitled to having power over someone else and that they should go along with whatever you do because you provide them with money. And that's most definitely not how a parent should think.
2) Remember that she doesn't have much of an idea of what is going on exactly. From her perspective, Kiko and her Dad are just fooling around, and they've kept lying to her and playing her for a fool to keep it under wraps. Now that she's realized it, how could she trust them? Obviously she's going to lash out and feel like she can't believe either of them anymore. Also, Dad is horrible at communicating. Instead of talking to his daughter about his problems, he'd rather play the part of the responsible parent, even though he keeps cracking under pressure and lying to save face. Not once has he tried to open up to his daughter about how much he's hurting, how hellish work is, how lost he feels as a widower and a parent, etc. By contrast, Miya has undertaken efforts to better herself (going back to school and studying hard to make up for lost time) and has communicated with her Dad about her issues.
As a side note, remember that Dad's pressure appears to be mostly self-imposed. His workaholic attitude and straight-laced behavior have made him something of a joke at work, where even his colleagues think he's being excessive, to the point that he's soft-banned from events and parties due to being such a stick in the mud. Does he actually need to put himself through so much pressure? The story has never indicated so. He keeps complaining about his colleagues being irresponsible and carefree, but he himself is stubbornly carrying on as a workaholic, seemingly without ever questioning how destructive his attitude is.
3) Miya remained in her room for so long because she was having a very hard time coping with her mother's death and felt like she couldn't communicate with her father. It wasn't because she "didn't feel like doing better" or something. During that time, Dad isn't shown to have gone through particular efforts to build bridges with her, except by cooking her food and knocking on her door every now and then. Meanwhile, Dad has kept on stubbornly refusing to speak out about his own issues, and hasn't undertaken any efforts to discourage Kiko's affections. Heck, even though he can very obviously see that Kiko's situation at home is far from ideal and has gotten strong hints that her mother is, not to put too fine a point on it, a psycho, he hasn't done anything to understand her or help her. Where Miya has been a passive victim of her own hurting and has been addressing it, Dad has been more actively complicit of it, going along with Kiko's advances, never actually saying: "This will not happen, we need to talk."
I'm not saying Miya is completely innocent, and she certainly isn't helping matters, but of everyone included, she feels the most like a victim to me, while Dad feels the most irresponsible of the bunch.
Of course, the best thing for everyone involved would be to sit down and talk about everything, instead of carrying on with unsaid truths, repressed grudges, and unhealthy delusions... but whether that will happen or not is anyone's guess.