I dont honestly know how far along she is have taken her in as part of my spay/neuter/shots project, so that she will have a safe place to be she was a stray that a lady called me on i know she is very big and believe she will have her babies soon.
Well, after the usual sixty-plus days of pregnancy, your kitty will begin to act strangely. She will start snooping around, looking for the perfect place to bring her newborns into the world. Most set up a birthing box. This birthing box serves not only as a place for mother to have her kittens in, but a safe spot for her to care for them until they're old enough to run around on their own. This box should be in an out-of-the-way place that you can get to, if necessary, but where cat and kittens will have plenty of needed privacy. So, you might want to provide her with alternatives for the Litterbox. Good luck and you are soing a wonderful thing.
I agree with Hell603. She has selected the litter box for her "safe place" to have her kittens. When my friend's cat was pregnant, I told her to provide a box for her, and the cat took that box as her place for the kittens to be born in and raised.
Sounds like she's gettin' ready. You can try putting a laundry basket or large tupperware container in a quiet place. She will probably find that much more suitable