My cat is 9 months old and pregnant?

Will she be okay with this litter. She has had all of her shots and is very healthy and average sized. She got pregnant with her first heat. No I didn't let her out, I had a stray come in through my rafters. I know it sounds crazy, but where my A/C unit is inside, I can look up into the attic. I was sitting in my living room, and my kids said that there was a different cat in the apartment. I didn't get her fixed, because she never goes outside, I never figured a cat would get inside. She keeps getting bigger and bigger, and I can feel little kicks every now and again. I'm just worried because she isn't even a year old. I also don't know when she is going to go in labor, because, I don't know how long she's been pregnant. I also don't know how long that cat had been in the house because we had been gone all day. Yes I know I need to get my cat fixed, so I would appreciate it if I didn't get the riot act because she isn't already fixed. I just want to know if anyone else has had this happen and if their cat was okay.