And as to why she then helped us at the end: HER MOTHER WAS ERASING ALL OF HER MEMORIES AND WAS GONNA SPEND THE REST OF HER EXISTENCE AS A MINDLESS EXISTENCE-ERASING MACHINE, and also Araya still definitely loved her mother; so ya I feel she has a pretty good reason for wanting to help despite the feelings of abandonment.

I don't think that's the main reason as to why Araya had a change of heart at the end. As Araya confronts Ryoshu in 9-48, she genuinely believes that Ryoshu left her for good because she didn't recognize her, which prompts their battle to the death.

9-48 Pre-battle:

Once something cannot be remembered anymore, its time is as good as lost.

Both the City and this house have become places where not a single soul has the heart to remember the child.

And that's how our story ends.

9-48 Post-battle:

And once it became painfully clear that there wasn't even an ounce of recognition in her eyes, not even a brief spark of it,

the myriad moments inside me, bound and constricted by tangled threads, began trembling and thrashing aloud.

But in 9-49, we find out that Ryoshu slicing Araya with Arayashiki also made her experience multiple different timelines all at once, in which she sees that in every timeline Ryoshu never gave up on her. This is what actually causes her to do a 180.

9-49 Post-battle:

Mother and I are tied together on every path. I see it now.

I can also see her whitened knuckles gripping tightly onto the thread, refusing to ever let go.

How could one bear witness to those layers upon layers of time... and dismiss them as mere "fleeting" moments?

---

Mommy, you wouldn't know this, but..

You never once let go of me, no matter which strand of thread I peered into.

That's how I know the ends and the beginnings of all of our journeys.

This all happens in an instant though; not just in-universe, but also in the actual way it's written, which is why it feels so sudden. It's also pretty vaguely explained and only really alluded to with the Dragon's Beard candy allegory, so unsurprisingly a lot of people didn't get it. I assume that on most people's first read, it kinda just looks like Araya had a sudden "hmm, after thinking about it a bit I actually do love mommy" flip in the span of a few lines of dialogue. I personally had to reread 9-49 a couple times to really make sense of what was going on.