Is it ok for a pregnant cat to feed kittens?

Momma cat had six kittens. Momma cat dissapeared about a week ago and I started taking care of the kittens myself. I have tried my very best to feed them and keep them clean. Unfortunately, two kittens died today. However my other cat is also pregnant. I was afraid of more kittens perishing. As a desperate attempt, I introduced my other cat to the kittens and she accepted the task and starting taking care of the kittens. This made me happy but, I'm just wondering if this will affect her pregnancy? Will she be fine feeding three week old kittens while she is still pregnant? What cautions would you recommend to take? Being a momma cat is no easy job. Thanks in advance