Feral 7 mo. old who is new, is attacking my 8 yr. old cat

One month ago a 7 mo. old showed up in our garage and I started feeding her. I brought her inside when it was raining or cold and she got along fine w/my 8 yr. old neutered male cat. 2 wks. later I took her to the vet to determine age/sex etc. When I found out she was female I brought her back the next day to be spayed. Unfortunately, she was pregnant. When I brought her home, my cat tried to be nice(giving her plenty of space, mewing when she hissed at him, etc.) Even when she was feeling better and would attack him, he would backoff. I rubbed a sock on my cats face to let the kitten smell him. Now, she still attacks him and even tries to go through the window at him if she see's him outside. Everytime she does this I put her in a closed off area for an hour. Any suggestions would be great. Thank you and God bless.