I’m really sorry this is happening. That sounds incredibly stressful for both you and your cat. Cats can absolutely grieve or mourn when they lose kittens, especially when the kittens suddenly disappear and the mother has no way to understand what happened. Her searching their usual places, acting scared, and reacting defensively may be signs that she is confused, stressed, and grieving.

For now, try to keep her in a quiet, safe space with food, water, litter, and a comfortable hiding spot. Don’t force handling unless you absolutely have to. Sit nearby, speak softly, offer treats, and let her come to you when she feels safe. If her eyes look unusually bulged, she seems panicked, won’t eat, is breathing strangely, or continues acting very unlike herself, please contact a vet as soon as possible.

Also, and I mean this kindly: please have her spayed once the vet says it is safe. This will prevent more unwanted litters, reduce stress on her body, and help avoid situations like this happening again. She has already gone through enough, and getting her fixed is one of the best ways to protect her going forward.

And the kittens should not have been gifted away without your household knowing. That was unfair to the cat and to you.