If Moo wants cute kittens for her brat, she can go to a shelter and get some because I guarantee you every shelter is going to be stuffed with kittens because it's going to be "kitten season" soon. But oh, that would cost adoption fees and Mommy probably isn't interested in paying money when she could just throw the unaltered female cat outside and get her pregnant for free. And I highly doubt Moo will pay to get all those kittens spayed/neutered when they reach sexual maturity. She probably won't find homes for them either - she'll just toss them outside like trash, where they will proceed to breed like crazy and repeatedly too. All you need is two unaltered cats to start an entire colony of inbred strays.
Who is to say the cat will come back? It could get hit by a car, it could have kittens in some random place, it could be picked up and adopted by someone else, it could be killed by a neighbor that hates cats (I know people in my old neighborhood frequently shot/poisoned strays for peeing in their yards), it could get sick and die from natural causes, or a million other things. What happens if the mom cat decides she wants to be CF and abandons the litter? Moo will probably just let the kittens starve because neither she nor her kid will have the patience and most likely not the money to hand-feed a whole litter every day.
Yes, kittens are adorable. I remember my family taking in a few pregnant female cats when I was a kid and those kittens were cute (I kept two of them too), but if the kid isn't even interested in a cat to begin with, why make more just for her? Is this Moo's way of getting out of having the birds and the bees talk with her kid or something?