Like what's up with my cat?

so, i have a pet cat that just gave birth to 3 healthy kittens 3+weeks ago. She was feeding them and was being a very good mother to her litter of kittens. Then, just 2 days ago, she started to act really strange and she was basically dragging her kittens all over the house, no idea why she was doing so. And then, when my mum went to check up on the cats a while later, all 3 kittens were missing and their mum wasn't even at all concerned to go look for them. She was basically sleeping all day long and it didnt even occur to her to go and feed the kittens. She showed no sign that she was at all concerned that her kittens were missing. We've searched all over the house and the neighbouring houses, but we cant seem to locate the kittens anywhere. Did she do something to her own kittens? Im really worried, the kittens are only 3+weeks old.
Added (1). meow: the mum is an adult stray cat, we decided to take her in as she was pregnant. And we cant keep an eye on her at all times, she must have sneaked out when we weren't looking. We were worried about the kittens, so obviously we searched every nook and cranny- including our neighbours house. Btw, you should direct the last question to yourself.

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