I took a stray a couple of weeks ago and had her spayed. She had kittens about 6 weeks prior, but they all died. There is another female stray that had kittens about 5 weeks ago. We have been holding them and taking care of these kittens in hopes of being able to find them homes as soon as they are ready. I noticed today that the one I had spayed a couple of weeks ago was picking up the kittens. These kittens belong to the other female. Why is the one that is not their mother picking them up. I make her put them down because I'm afraid she will hurt them or try and take them off. Should I be worried?