Right, they have the vet smells on them now and smell strange to her. You can try using the vanilla extract trick. Dab Mum and kittens with vanilla extract under the chin, between the shoulders and at the base of the tail. This helps everyone to smell the same.
You can also get a towel, rub Mumcat well with it to get her scent on it and then rub each kitten with the towel to transfer the scent. Even better is to use the towel or blanket that she normally sleeps on.
I know a breeder who had to do a kitten swap in a litter. The problem is the new mom wanted nothing to do with the new kitten in her litter. So she rubbed wet food over the kitten to get mom to lick her clean. This got moms smell all over the kitten and all was fine.
But at 4 months old the kittens will be fine without moms help.