She may have diarrhea from eating the placentas, but it can't be helped under the circumstances. Normally eating a few is ok and then we remove them with house cats. Don't worry about it now. They just can't stay inside her or she will be ill with infection.
No, all cats eat placentas. Yes, in the wild they eat them all so that predators do not pick up the scent. It's okay. Does it seem like there is one more? Has she stopped to drink kitty milk or anything?