Kin Control specifies being able to control all descendants, but I don't think Ariel ever even tried to control Kumoko. Was she not able to?
The answer to this is: she probably could have, but not anymore. The description for the Kin Control skill specifies descendants, not children (though I am going by the English version). However, controlling far removed descendants may be more difficult, and it may be a requirement that there be a living link to them. I think this because after Mother is killed, Kumoko says this, which confirms there's no longer a link between them, on page 224 of volume 4:
I successfully overthrew Mother.
Consequently, the Parallel Minds that were fighting her soul have come back to me.
At the same time, Mother's control over me vanishes completely, and the faint connection I felt before disappears.
In other words, there's no longer anyone trying to control me, and my link to the network of spider souls that centered around Mother is gone.
The Demon Lord was the real origin of this network, but since I was on the fringes, connecting to her via Mother, that means I'm cut off from the Demon Lord now.
The problem is, that means I can't attack her soul with my Parallel Minds like I did with Mother.
Without a connection, I can't send Parallel Minds over to her.
And when her Parallel Minds inform her that Body Brain already went over to the Demon Lord while the connection was still active:
Wait, but isn't my connection to the Demon Lord gone now?
Huh? Is former body brain going to be able to come back?
Um, I'm pretty sure she can't, right?
'Cause, like, the connection is gone now.
Whatever the case for other spiders, Kumoko cannot be controlled by Ariel because there is no longer a link between them. It's unclear how much that has to do with Heresy Nullification. That being "on the fringes" of the network comment might have to do with this skill, and not just that she's not a direct descendant of Ariel. It's worth noting that of all the spiders that attacked Kumoko, only the puppet spiders were mentioned of having been directly under Ariel's control. All the other ones, probably all natives of the Great Elroe Labyrinth and probably Mother's children, were controlled by Mother. Ariel not taking direct control of any of Mother's children may either indicate she can't, and instead can only issue orders through Mother, or it could just mean nothing, and she just allows Mother to give orders because splitting the workload is the best strategy.
Additionally, there's a point at which Kumoko also comments that changing her species (through evolution) probably weakened Mother's ability to control her.