It took me a minute or two after reading this chapter, but you know, I think I actually really like this move from the author. It doesn't drag out the mystery of her cryptic seemingly-contradictory statements, and really, where was the story going to go if she was just Hasshaku-sama? She's starting to get a decent grasp of what her power is/are, she's starting to really iron out her relationship with Seiichiro, so where does the story go from there?
This move potentially lets the author, should they choose to do so, shift the story balance from being about Seiichiro and his relationship with her, to being about her and her relationship with her nature. It allows the author to gradually resolve conflicts coming from the nature of this couple's relationship while still preserving/introducing relevant conflict to the story, allowing the romantic relationship to progress without reaching a natural conclusion at this point.
I briefly wondered if the phone call on page 10 is referring to her mother or her uncle's mother (i.e. her paternal grandmother, very different implications if it's the former) but it's clear that she's not in close contact with her mother, otherwise Hasshaku-sama could probably just tell Yachiru-san so much about her powers. It seems like the obvious way to get some answers, rather than this roundabout way of testing things with Seiichiro.
(also, amusing as it might be to joke about her father's death-by-SnuSnu, I don't think the timing works out there, judging by when she started living with her uncle. But it might be relevant somehow? At this point her father's death is a potential future plot point, although I wouldn't go so far as to say it's a Chekov's Gun)
So, are we going to get a joint quest from the two, looking for her mother to get some answers while they continue trying to learn about her nature? And obviously her mother might know a thing or two about relationships between yokai and humans.
Solid move from the author, I respect it. Much better than lengthening a story via perpetual/cyclical ambiguity or adding a second love interest.
Edit: re: her clothes, I think 1) obviously they do change in scale, otherwise this wouldn't be a question in the first place. Unless, maybe they're just "slow", and the rate of change is different sometimes? 2) was this genius planning from the beginning, or is this a clever way to cover up the art not being 100% consistent / accurate in scaling 3) if her clothes grow, why can't they "keep up" with her pace of growing? 4) does this mean other inanimate (or animate) objects in contact or very close proximity with her would scale too? Would a bucket of water or block of plutonium scale? There's some tricky ironworking tasks that could use an ability like that.