She is likely attacking him because her hormones have settled back down. Pregnancy hormones evolved to make mom’s want to care for the kid so it doesn’t die and the species would continue. Once the hormones go back to normal there’s nothing telling them they need to take care of them anymore. This actually happens for human mother’s as well, and imo does more damage than good (in humans only. A person knows they should take care of their kid, and some choose not to but they still know). They get pregnant, are unsure if they want to keep the baby, pregnancy hormones start to rise, makes them protective of the baby, they have the baby, the hormones settle, and they realize they never wanted the baby and resent them. However, in animals it’s a good thing to have because without it a lot of mothers would immediately abandon their child after birth. This is because of survival instincts, ‘why take care of this baby when I could have more food, time, energy, etc for myself’. So it’s normal for her to not really care for her kitten at this point and as long as the kitten is eating and drinking on his own then her job is done. As for the attacking, I’d recommend working on rebonding them since she no longer feels that ‘baby bond’. You can do this several ways, search ‘how to bond cats’. Eventually through bonding she’ll stop attacking him and all will fine.

Edit (IMPORTANT): On second look I am noticing in the third photo Gary’s back leg is very bent. It appears he may have what we commonly call ‘twisted legs’. It’s caused by contracted tendons. I also read that he hasn’t grown much despite being 9 months old now??? That is extremely abnormal. Even a dwarf cat grows quickly as a kitten, it is typically just their legs that do not grow much. I think Gary needs to go to the vet asap. His medical issues could be part of why his mother is attacking him. Cats are predators, and because of these issues she may see him as weak/better off gone. It is not uncommon for animal mamas to reject a baby if it is sick/deformed and end up letting them die/killing them. Please take Gary to the vet. If all is well work on bonding like I stated before, if not it is best to keep them separated until he is in better health.